<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019ff2d2-756d-79a0-8073-6c386a4e2d0c,g:a18c5746-d133-46fb-a0dd-f0194f4346be-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.iridium.com/role/DocumentAndEntityInformation" xlink:type="simple" xlink:href="irdm-20260930.xsd#DocumentAndEntityInformation"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/DocumentAndEntityInformation" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_019ff2d2-7625-7132-9d5a-8566c19aa59a" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_DocumentInformationTable_019ff2d2-7625-7132-9d5a-8566c19aa59a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ff2d2-7625-7e39-84dc-223e44169072" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_019ff2d2-7625-7132-9d5a-8566c19aa59a" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ff2d2-7625-7e39-84dc-223e44169072" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-7e39-84dc-223e44169072_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ff2d2-7625-7e39-84dc-223e44169072" xlink:to="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-7e39-84dc-223e44169072_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-75b9-a6e1-97879120c6b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ff2d2-7625-7e39-84dc-223e44169072" xlink:to="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-75b9-a6e1-97879120c6b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ff2d2-7625-7b87-b7ae-386baf216c9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-75b9-a6e1-97879120c6b0" xlink:to="loc_us-gaap_CommonStockMember_019ff2d2-7625-7b87-b7ae-386baf216c9a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityListingsExchangeAxis_019ff2d2-7625-7948-a192-dbddd1c1146c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityListingsExchangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_dei_DocumentInformationTable_019ff2d2-7625-7132-9d5a-8566c19aa59a" xlink:to="loc_dei_EntityListingsExchangeAxis_019ff2d2-7625-7948-a192-dbddd1c1146c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_ExchangeDomain_019ff2d2-7625-7948-a192-dbddd1c1146c_default" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_ExchangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_EntityListingsExchangeAxis_019ff2d2-7625-7948-a192-dbddd1c1146c" xlink:to="loc_dei_ExchangeDomain_019ff2d2-7625-7948-a192-dbddd1c1146c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_ExchangeDomain_019ff2d2-7625-7c91-8b13-2d22e67e9b92" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_ExchangeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_EntityListingsExchangeAxis_019ff2d2-7625-7948-a192-dbddd1c1146c" xlink:to="loc_dei_ExchangeDomain_019ff2d2-7625-7c91-8b13-2d22e67e9b92" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_exch_XNGS_019ff2d2-7625-72eb-9a21-0b43ed886f9b" xlink:href="https://xbrl.sec.gov/exch/2026/exch-2026.xsd#exch_XNGS"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_ExchangeDomain_019ff2d2-7625-7c91-8b13-2d22e67e9b92" xlink:to="loc_exch_XNGS_019ff2d2-7625-72eb-9a21-0b43ed886f9b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityRegistrantName_019ff2d2-7625-7a07-8e53-20a28625a339" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityRegistrantName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityRegistrantName_019ff2d2-7625-7a07-8e53-20a28625a339" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_019ff2d2-7625-718c-b8e3-4b4128591ab4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCentralIndexKey"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityCentralIndexKey_019ff2d2-7625-718c-b8e3-4b4128591ab4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CurrentFiscalYearEndDate_019ff2d2-7625-7586-99f8-b6f2be4cfb8c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CurrentFiscalYearEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_CurrentFiscalYearEndDate_019ff2d2-7625-7586-99f8-b6f2be4cfb8c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFilerCategory_019ff2d2-7625-7486-8452-2f1f1d003f6b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFilerCategory"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityFilerCategory_019ff2d2-7625-7486-8452-2f1f1d003f6b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_019ff2d2-7625-72d3-83ee-73ba2280d474" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_TradingSymbol"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_TradingSymbol_019ff2d2-7625-72d3-83ee-73ba2280d474" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCurrentReportingStatus_019ff2d2-7625-7b9e-9106-9fc2ec1f5761" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCurrentReportingStatus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityCurrentReportingStatus_019ff2d2-7625-7b9e-9106-9fc2ec1f5761" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentQuarterlyReport_019ff2d2-7625-760d-9011-b17b6c9371e4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentQuarterlyReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_DocumentQuarterlyReport_019ff2d2-7625-760d-9011-b17b6c9371e4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentType_019ff2d2-7625-7952-a405-f6ffe5bbc974" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentType"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_DocumentType_019ff2d2-7625-7952-a405-f6ffe5bbc974" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_019ff2d2-7625-72f4-847c-2055908be82e" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_AmendmentFlag"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_AmendmentFlag_019ff2d2-7625-72f4-847c-2055908be82e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntitySmallBusiness_019ff2d2-7625-761e-982f-751fdad8afe2" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntitySmallBusiness"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntitySmallBusiness_019ff2d2-7625-761e-982f-751fdad8afe2" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_019ff2d2-7625-7f90-8f79-86988d5d765f" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityEmergingGrowthCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityEmergingGrowthCompany_019ff2d2-7625-7f90-8f79-86988d5d765f" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityShellCompany_019ff2d2-7625-7622-81ac-be444d8bd715" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityShellCompany"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityShellCompany_019ff2d2-7625-7622-81ac-be444d8bd715" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentPeriodEndDate_019ff2d2-7625-7ac0-aee6-f1fe6c289656" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentPeriodEndDate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_DocumentPeriodEndDate_019ff2d2-7625-7ac0-aee6-f1fe6c289656" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalPeriodFocus_019ff2d2-7625-7703-8f9a-b0c8af97c36d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalPeriodFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_DocumentFiscalPeriodFocus_019ff2d2-7625-7703-8f9a-b0c8af97c36d" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentFiscalYearFocus_019ff2d2-7625-7e29-b1b8-17e4ee53e965" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentFiscalYearFocus"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_DocumentFiscalYearFocus_019ff2d2-7625-7e29-b1b8-17e4ee53e965" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressAddressLine1_019ff2d2-7625-7206-af57-453131066848" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressAddressLine1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityAddressAddressLine1_019ff2d2-7625-7206-af57-453131066848" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressCityOrTown_019ff2d2-7625-7154-8b2b-7d09e7dafaf5" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressCityOrTown"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityAddressCityOrTown_019ff2d2-7625-7154-8b2b-7d09e7dafaf5" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressStateOrProvince_019ff2d2-7625-7392-910a-13dbb53e2124" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressStateOrProvince"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityAddressStateOrProvince_019ff2d2-7625-7392-910a-13dbb53e2124" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityAddressPostalZipCode_019ff2d2-7625-70b2-913c-3da2bff2ae7d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityAddressPostalZipCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityAddressPostalZipCode_019ff2d2-7625-70b2-913c-3da2bff2ae7d" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentTransitionReport_019ff2d2-7625-7c0b-941a-a2c9d0e3c37c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentTransitionReport"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_DocumentTransitionReport_019ff2d2-7625-7c0b-941a-a2c9d0e3c37c" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_CityAreaCode_019ff2d2-7625-7282-b76a-a8e47ed9ce9b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_CityAreaCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_CityAreaCode_019ff2d2-7625-7282-b76a-a8e47ed9ce9b" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LocalPhoneNumber_019ff2d2-7625-7e9c-b808-6df7f2118ae0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_LocalPhoneNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_LocalPhoneNumber_019ff2d2-7625-7e9c-b808-6df7f2118ae0" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_019ff2d2-7625-74c5-b25e-bb4675980ea0" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityFileNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityFileNumber_019ff2d2-7625-74c5-b25e-bb4675980ea0" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_019ff2d2-7625-7381-912a-6da4ad733325" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityIncorporationStateCountryCode"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityIncorporationStateCountryCode_019ff2d2-7625-7381-912a-6da4ad733325" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityInteractiveDataCurrent_019ff2d2-7625-7637-8535-c468867a6fe4" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityInteractiveDataCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityInteractiveDataCurrent_019ff2d2-7625-7637-8535-c468867a6fe4" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_019ff2d2-7625-76ad-a1e8-76611832f1f9" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SecurityExchangeName"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_SecurityExchangeName_019ff2d2-7625-76ad-a1e8-76611832f1f9" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_019ff2d2-7625-7f94-8cea-c0871b1e7f6b" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_Security12bTitle"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_Security12bTitle_019ff2d2-7625-7f94-8cea-c0871b1e7f6b" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019ff2d2-7625-7dd6-a929-56665e78bb69" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019ff2d2-7625-7dd6-a929-56665e78bb69" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCommonStockSharesOutstanding_019ff2d2-7625-77ae-b7e5-a4a79cb4b4e8" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityCommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityCommonStockSharesOutstanding_019ff2d2-7625-77ae-b7e5-a4a79cb4b4e8" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_019ff2d2-7625-75dc-8a2b-e251043dc33d" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_EntityTaxIdentificationNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_019ff2d2-7625-7b2c-a9cd-8e0492982bdc" xlink:to="loc_dei_EntityTaxIdentificationNumber_019ff2d2-7625-75dc-8a2b-e251043dc33d" xlink:type="arc" order="29"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/CondensedConsolidatedBalanceSheets" xlink:type="simple" xlink:href="irdm-20260930.xsd#CondensedConsolidatedBalanceSheets"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/CondensedConsolidatedBalanceSheets" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ff2d2-7625-7536-a83e-31e72d4e9a8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ff2d2-7625-7818-a42c-4029675c1a8e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7536-a83e-31e72d4e9a8e" xlink:to="loc_us-gaap_StatementTable_019ff2d2-7625-7818-a42c-4029675c1a8e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ff2d2-7625-7742-a669-980381387e2d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ff2d2-7625-7818-a42c-4029675c1a8e" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ff2d2-7625-7742-a669-980381387e2d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-7742-a669-980381387e2d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ff2d2-7625-7742-a669-980381387e2d" xlink:to="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-7742-a669-980381387e2d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-7e09-9403-525fa02846ce" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ff2d2-7625-7742-a669-980381387e2d" xlink:to="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-7e09-9403-525fa02846ce" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ff2d2-7625-75b1-913e-511e749bb9a2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-7e09-9403-525fa02846ce" xlink:to="loc_us-gaap_CommonStockMember_019ff2d2-7625-75b1-913e-511e749bb9a2" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsAbstract_019ff2d2-7625-726f-b824-627005a0534e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7536-a83e-31e72d4e9a8e" xlink:to="loc_us-gaap_AssetsAbstract_019ff2d2-7625-726f-b824-627005a0534e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrentAbstract_019ff2d2-7625-763a-8234-3349652ec6eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ff2d2-7625-726f-b824-627005a0534e" xlink:to="loc_us-gaap_AssetsCurrentAbstract_019ff2d2-7625-763a-8234-3349652ec6eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019ff2d2-7625-7ae2-a945-17687933fc83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019ff2d2-7625-763a-8234-3349652ec6eb" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019ff2d2-7625-7ae2-a945-17687933fc83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableNetCurrent_019ff2d2-7625-7ac4-8d11-1344f7d722e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableNetCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019ff2d2-7625-763a-8234-3349652ec6eb" xlink:to="loc_us-gaap_AccountsReceivableNetCurrent_019ff2d2-7625-7ac4-8d11-1344f7d722e4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InventoryNet_019ff2d2-7625-7271-b94b-2b29e9228064" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InventoryNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019ff2d2-7625-763a-8234-3349652ec6eb" xlink:to="loc_us-gaap_InventoryNet_019ff2d2-7625-7271-b94b-2b29e9228064" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019ff2d2-7625-7f7e-8f61-230dcb679694" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PrepaidExpenseAndOtherAssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019ff2d2-7625-763a-8234-3349652ec6eb" xlink:to="loc_us-gaap_PrepaidExpenseAndOtherAssetsCurrent_019ff2d2-7625-7f7e-8f61-230dcb679694" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetsCurrent_019ff2d2-7625-7a5a-9d7d-2e1a07cfabf8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AssetsCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsCurrentAbstract_019ff2d2-7625-763a-8234-3349652ec6eb" xlink:to="loc_us-gaap_AssetsCurrent_019ff2d2-7625-7a5a-9d7d-2e1a07cfabf8" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019ff2d2-7625-76de-809e-68bcb917d30e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ff2d2-7625-726f-b824-627005a0534e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019ff2d2-7625-76de-809e-68bcb917d30e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_019ff2d2-7625-73b6-b44e-f97660b230bb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ff2d2-7625-726f-b824-627005a0534e" xlink:to="loc_us-gaap_EquityMethodInvestments_019ff2d2-7625-73b6-b44e-f97660b230bb" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherAssetsNoncurrent_019ff2d2-7625-71ba-aef4-16ca88295e35" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherAssetsNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ff2d2-7625-726f-b824-627005a0534e" xlink:to="loc_us-gaap_OtherAssetsNoncurrent_019ff2d2-7625-71ba-aef4-16ca88295e35" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019ff2d2-7625-7897-acfe-cdd8f57c190a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ff2d2-7625-726f-b824-627005a0534e" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019ff2d2-7625-7897-acfe-cdd8f57c190a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019ff2d2-7625-7ed8-83e9-a9df68587152" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ff2d2-7625-726f-b824-627005a0534e" xlink:to="loc_us-gaap_Goodwill_019ff2d2-7625-7ed8-83e9-a9df68587152" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Assets_019ff2d2-7625-763d-bc81-25d386fcc6d2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Assets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AssetsAbstract_019ff2d2-7625-726f-b824-627005a0534e" xlink:to="loc_us-gaap_Assets_019ff2d2-7625-763d-bc81-25d386fcc6d2" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ff2d2-7625-7c72-a3a3-f11f3d7ea5cd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7536-a83e-31e72d4e9a8e" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ff2d2-7625-7c72-a3a3-f11f3d7ea5cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrentAbstract_019ff2d2-7625-7d71-8568-f446878e7b56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrentAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ff2d2-7625-7c72-a3a3-f11f3d7ea5cd" xlink:to="loc_us-gaap_LiabilitiesCurrentAbstract_019ff2d2-7625-7d71-8568-f446878e7b56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LinesOfCreditCurrent_019ff2d2-7625-7a68-bc7f-cf8b505f32b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LinesOfCreditCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019ff2d2-7625-7d71-8568-f446878e7b56" xlink:to="loc_us-gaap_LinesOfCreditCurrent_019ff2d2-7625-7a68-bc7f-cf8b505f32b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsPayableCurrent_019ff2d2-7625-7413-b0cd-b4000acb9915" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsPayableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019ff2d2-7625-7d71-8568-f446878e7b56" xlink:to="loc_us-gaap_AccountsPayableCurrent_019ff2d2-7625-7413-b0cd-b4000acb9915" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccruedLiabilitiesCurrent_019ff2d2-7625-7edb-8fdb-12033bb23f4d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccruedLiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019ff2d2-7625-7d71-8568-f446878e7b56" xlink:to="loc_us-gaap_AccruedLiabilitiesCurrent_019ff2d2-7625-7edb-8fdb-12033bb23f4d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRevenueCurrent_019ff2d2-7625-7798-a129-e82dbcc9c2a4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredRevenueCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019ff2d2-7625-7d71-8568-f446878e7b56" xlink:to="loc_us-gaap_DeferredRevenueCurrent_019ff2d2-7625-7798-a129-e82dbcc9c2a4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesCurrent_019ff2d2-7625-7e7d-945a-08350e54b0a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesCurrentAbstract_019ff2d2-7625-7d71-8568-f446878e7b56" xlink:to="loc_us-gaap_LiabilitiesCurrent_019ff2d2-7625-7e7d-945a-08350e54b0a1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermLineOfCredit_019ff2d2-7625-74d2-9c44-6b8fdd18521d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermLineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ff2d2-7625-7c72-a3a3-f11f3d7ea5cd" xlink:to="loc_us-gaap_LongTermLineOfCredit_019ff2d2-7625-74d2-9c44-6b8fdd18521d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019ff2d2-7625-76fb-b515-1b7d1497b780" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxLiabilitiesNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ff2d2-7625-7c72-a3a3-f11f3d7ea5cd" xlink:to="loc_us-gaap_DeferredIncomeTaxLiabilitiesNet_019ff2d2-7625-76fb-b515-1b7d1497b780" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredRevenueNoncurrent_019ff2d2-7625-732d-b317-622cef2e9812" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredRevenueNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ff2d2-7625-7c72-a3a3-f11f3d7ea5cd" xlink:to="loc_us-gaap_DeferredRevenueNoncurrent_019ff2d2-7625-732d-b317-622cef2e9812" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherLiabilitiesNoncurrent_019ff2d2-7625-74e5-aed0-d458b5ec392c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherLiabilitiesNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ff2d2-7625-7c72-a3a3-f11f3d7ea5cd" xlink:to="loc_us-gaap_OtherLiabilitiesNoncurrent_019ff2d2-7625-74e5-aed0-d458b5ec392c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Liabilities_019ff2d2-7625-74e6-b15e-025dc8d4667a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Liabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ff2d2-7625-7c72-a3a3-f11f3d7ea5cd" xlink:to="loc_us-gaap_Liabilities_019ff2d2-7625-74e6-b15e-025dc8d4667a" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommitmentsAndContingencies_019ff2d2-7625-7006-96a0-d7215572a8e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommitmentsAndContingencies"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ff2d2-7625-7c72-a3a3-f11f3d7ea5cd" xlink:to="loc_us-gaap_CommitmentsAndContingencies_019ff2d2-7625-7006-96a0-d7215572a8e0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquityAbstract_019ff2d2-7625-72e1-aaed-f064c0ef9a78" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquityAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ff2d2-7625-7c72-a3a3-f11f3d7ea5cd" xlink:to="loc_us-gaap_StockholdersEquityAbstract_019ff2d2-7625-72e1-aaed-f064c0ef9a78" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockValue_019ff2d2-7625-77a1-bb9a-40ace866b218" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019ff2d2-7625-72e1-aaed-f064c0ef9a78" xlink:to="loc_us-gaap_CommonStockValue_019ff2d2-7625-77a1-bb9a-40ace866b218" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019ff2d2-7625-7f9b-8782-661bf4e99e23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019ff2d2-7625-72e1-aaed-f064c0ef9a78" xlink:to="loc_us-gaap_AdditionalPaidInCapitalCommonStock_019ff2d2-7625-7f9b-8782-661bf4e99e23" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019ff2d2-7625-7a4d-bbbc-f01809367dca" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsAccumulatedDeficit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019ff2d2-7625-72e1-aaed-f064c0ef9a78" xlink:to="loc_us-gaap_RetainedEarningsAccumulatedDeficit_019ff2d2-7625-7a4d-bbbc-f01809367dca" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019ff2d2-7625-767d-8f71-4b75f0bc1c46" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019ff2d2-7625-72e1-aaed-f064c0ef9a78" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossNetOfTax_019ff2d2-7625-767d-8f71-4b75f0bc1c46" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ff2d2-7625-737d-9783-ef2aa2ae0049" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StockholdersEquityAbstract_019ff2d2-7625-72e1-aaed-f064c0ef9a78" xlink:to="loc_us-gaap_StockholdersEquity_019ff2d2-7625-737d-9783-ef2aa2ae0049" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LiabilitiesAndStockholdersEquity_019ff2d2-7625-79b7-a253-f657d12b71f1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LiabilitiesAndStockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LiabilitiesAndStockholdersEquityAbstract_019ff2d2-7625-7c72-a3a3-f11f3d7ea5cd" xlink:to="loc_us-gaap_LiabilitiesAndStockholdersEquity_019ff2d2-7625-79b7-a253-f657d12b71f1" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="simple" xlink:href="irdm-20260930.xsd#CondensedConsolidatedBalanceSheetsParenthetical"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ff2d2-7625-7233-bae9-280987d167ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ff2d2-7625-7039-ac72-bdd07f30340d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7233-bae9-280987d167ab" xlink:to="loc_us-gaap_StatementTable_019ff2d2-7625-7039-ac72-bdd07f30340d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_019ff2d2-7625-7629-bed5-540f4fb5b0ab" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementClassOfStockAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ff2d2-7625-7039-ac72-bdd07f30340d" xlink:to="loc_us-gaap_StatementClassOfStockAxis_019ff2d2-7625-7629-bed5-540f4fb5b0ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-7629-bed5-540f4fb5b0ab_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ff2d2-7625-7629-bed5-540f4fb5b0ab" xlink:to="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-7629-bed5-540f4fb5b0ab_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-7351-8375-8435431457d8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementClassOfStockAxis_019ff2d2-7625-7629-bed5-540f4fb5b0ab" xlink:to="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-7351-8375-8435431457d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ff2d2-7625-78c4-99ce-cd446f1ad59f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_019ff2d2-7625-7351-8375-8435431457d8" xlink:to="loc_us-gaap_CommonStockMember_019ff2d2-7625-78c4-99ce-cd446f1ad59f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockParOrStatedValuePerShare_019ff2d2-7625-7666-8f46-bb28b06ccce7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7233-bae9-280987d167ab" xlink:to="loc_us-gaap_CommonStockParOrStatedValuePerShare_019ff2d2-7625-7666-8f46-bb28b06ccce7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_019ff2d2-7625-709e-9950-45755f0e784d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7233-bae9-280987d167ab" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_019ff2d2-7625-709e-9950-45755f0e784d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesIssued_019ff2d2-7625-7ea7-985a-d409970fa1fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7233-bae9-280987d167ab" xlink:to="loc_us-gaap_CommonStockSharesIssued_019ff2d2-7625-7ea7-985a-d409970fa1fc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019ff2d2-7625-7aff-8b26-3a9f51b8b4bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7233-bae9-280987d167ab" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019ff2d2-7625-7aff-8b26-3a9f51b8b4bf" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/CondensedConsolidatedStatementsofOperationsandComprehensiveIncome" xlink:type="simple" xlink:href="irdm-20260930.xsd#CondensedConsolidatedStatementsofOperationsandComprehensiveIncome"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/CondensedConsolidatedStatementsofOperationsandComprehensiveIncome" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ff2d2-7625-77db-9e65-21577bbdd19b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:to="loc_us-gaap_StatementTable_019ff2d2-7625-77db-9e65-21577bbdd19b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019ff2d2-7625-7743-9d4e-b81836f1311d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ff2d2-7625-77db-9e65-21577bbdd19b" xlink:to="loc_srt_ProductOrServiceAxis_019ff2d2-7625-7743-9d4e-b81836f1311d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7743-9d4e-b81836f1311d_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019ff2d2-7625-7743-9d4e-b81836f1311d" xlink:to="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7743-9d4e-b81836f1311d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-77f7-8afd-c5370feb1963" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019ff2d2-7625-7743-9d4e-b81836f1311d" xlink:to="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-77f7-8afd-c5370feb1963" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_019ff2d2-7625-71ac-9f4a-4348539f7507" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-77f7-8afd-c5370feb1963" xlink:to="loc_us-gaap_ServiceMember_019ff2d2-7625-71ac-9f4a-4348539f7507" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SubscriptionAndCirculationMember_019ff2d2-7625-780b-a348-9191589d966b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SubscriptionAndCirculationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-77f7-8afd-c5370feb1963" xlink:to="loc_us-gaap_SubscriptionAndCirculationMember_019ff2d2-7625-780b-a348-9191589d966b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_EngineeringandSupportServicesMember_019ff2d2-7625-76e2-93ed-82fddd982c43" xlink:href="irdm-20260930.xsd#irdm_EngineeringandSupportServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-77f7-8afd-c5370feb1963" xlink:to="loc_irdm_EngineeringandSupportServicesMember_019ff2d2-7625-76e2-93ed-82fddd982c43" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_019ff2d2-7625-7502-be10-9989d0e55d8d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:to="loc_us-gaap_RevenuesAbstract_019ff2d2-7625-7502-be10-9989d0e55d8d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ff2d2-7625-76d8-a78d-dcde218b6ad3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019ff2d2-7625-7502-be10-9989d0e55d8d" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ff2d2-7625-76d8-a78d-dcde218b6ad3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpensesAbstract_019ff2d2-7625-7d32-8512-74a30c0746f8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:to="loc_us-gaap_CostsAndExpensesAbstract_019ff2d2-7625-7d32-8512-74a30c0746f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfGoodsAndServicesSold_019ff2d2-7625-741c-8ee8-eba6351aedbe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostOfGoodsAndServicesSold"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019ff2d2-7625-7d32-8512-74a30c0746f8" xlink:to="loc_us-gaap_CostOfGoodsAndServicesSold_019ff2d2-7625-741c-8ee8-eba6351aedbe" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019ff2d2-7625-77a8-9748-df9cacebe874" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019ff2d2-7625-7d32-8512-74a30c0746f8" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019ff2d2-7625-77a8-9748-df9cacebe874" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019ff2d2-7625-7fa7-af29-e7852ff38a37" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019ff2d2-7625-7d32-8512-74a30c0746f8" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019ff2d2-7625-7fa7-af29-e7852ff38a37" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019ff2d2-7625-7bde-b2c1-99f49ec8d6af" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019ff2d2-7625-7d32-8512-74a30c0746f8" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019ff2d2-7625-7bde-b2c1-99f49ec8d6af" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_019ff2d2-7625-78c5-8590-b7477adfd798" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CostsAndExpensesAbstract_019ff2d2-7625-7d32-8512-74a30c0746f8" xlink:to="loc_us-gaap_CostsAndExpenses_019ff2d2-7625-78c5-8590-b7477adfd798" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019ff2d2-7625-7d05-946e-c0db719ca0c2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:to="loc_us-gaap_OperatingIncomeLoss_019ff2d2-7625-7d05-946e-c0db719ca0c2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019ff2d2-7625-7b45-b777-e5bf3f8f4f0d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:to="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019ff2d2-7625-7b45-b777-e5bf3f8f4f0d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestIncomeExpenseNet_019ff2d2-7625-7207-a0fa-213349da0b61" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestIncomeExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019ff2d2-7625-7b45-b777-e5bf3f8f4f0d" xlink:to="loc_us-gaap_InterestIncomeExpenseNet_019ff2d2-7625-7207-a0fa-213349da0b61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019ff2d2-7625-7be5-9b22-3c3a53649400" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019ff2d2-7625-7b45-b777-e5bf3f8f4f0d" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019ff2d2-7625-7be5-9b22-3c3a53649400" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019ff2d2-7625-7f18-8c01-0f0f26c7c0aa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019ff2d2-7625-7b45-b777-e5bf3f8f4f0d" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019ff2d2-7625-7f18-8c01-0f0f26c7c0aa" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_019ff2d2-7625-7def-bce8-8b731cb61649" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019ff2d2-7625-7b45-b777-e5bf3f8f4f0d" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesMinorityInterestAndIncomeLossFromEquityMethodInvestments_019ff2d2-7625-7def-bce8-8b731cb61649" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019ff2d2-7625-7529-9d0a-a8df64f1eb16" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019ff2d2-7625-7529-9d0a-a8df64f1eb16" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019ff2d2-7625-760d-a74b-99c6ddbb239a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019ff2d2-7625-760d-a74b-99c6ddbb239a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019ff2d2-7625-706b-8039-d607394a1070" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:to="loc_us-gaap_NetIncomeLoss_019ff2d2-7625-706b-8039-d607394a1070" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019ff2d2-7625-7084-b421-e46697f52a24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019ff2d2-7625-7084-b421-e46697f52a24" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019ff2d2-7625-7632-a5dc-a2c92b0c1f0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019ff2d2-7625-7632-a5dc-a2c92b0c1f0e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019ff2d2-7625-7d0b-a364-ea9a1ab0b15b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:to="loc_us-gaap_EarningsPerShareBasic_019ff2d2-7625-7d0b-a364-ea9a1ab0b15b" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019ff2d2-7625-7cbe-a717-355f6740029a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019ff2d2-7625-7cbe-a717-355f6740029a" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_019ff2d2-7625-773c-8bad-c5701d031111" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTaxAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-70f2-ae02-7dae94e22f42" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_019ff2d2-7625-773c-8bad-c5701d031111" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019ff2d2-7625-7831-a5f0-81703e68ddb4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_019ff2d2-7625-7489-9b6f-5026026456b6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_019ff2d2-7625-773c-8bad-c5701d031111" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_019ff2d2-7625-7489-9b6f-5026026456b6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_UnrealizedGainLossOnCashFlowHedgesNetOfTax_019ff2d2-7625-7bf5-b5d8-38405855444b" xlink:href="irdm-20260930.xsd#irdm_UnrealizedGainLossOnCashFlowHedgesNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_019ff2d2-7625-773c-8bad-c5701d031111" xlink:to="loc_irdm_UnrealizedGainLossOnCashFlowHedgesNetOfTax_019ff2d2-7625-7bf5-b5d8-38405855444b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ComprehensiveIncomeNetOfTax_019ff2d2-7625-7c1b-905e-28168dbe8d06" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ComprehensiveIncomeNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ComprehensiveIncomeNetOfTaxAbstract_019ff2d2-7625-773c-8bad-c5701d031111" xlink:to="loc_us-gaap_ComprehensiveIncomeNetOfTax_019ff2d2-7625-7c1b-905e-28168dbe8d06" xlink:type="arc" order="4"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/ConsolidatedStatementsofChangesinStockholdersEquityStatement" xlink:type="simple" xlink:href="irdm-20260930.xsd#ConsolidatedStatementsofChangesinStockholdersEquityStatement"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/ConsolidatedStatementsofChangesinStockholdersEquityStatement" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ff2d2-7625-7743-b336-a5ccdabf99b3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_us-gaap_StatementTable_019ff2d2-7625-7743-b336-a5ccdabf99b3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019ff2d2-7625-740c-a3c0-9309c60f7f94" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ff2d2-7625-7743-b336-a5ccdabf99b3" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019ff2d2-7625-740c-a3c0-9309c60f7f94" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ff2d2-7625-740c-a3c0-9309c60f7f94_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ff2d2-7625-740c-a3c0-9309c60f7f94" xlink:to="loc_us-gaap_EquityComponentDomain_019ff2d2-7625-740c-a3c0-9309c60f7f94_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019ff2d2-7625-7517-a394-02f90834d395" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019ff2d2-7625-740c-a3c0-9309c60f7f94" xlink:to="loc_us-gaap_EquityComponentDomain_019ff2d2-7625-7517-a394-02f90834d395" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019ff2d2-7625-7472-be27-84bf25c48e2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ff2d2-7625-7517-a394-02f90834d395" xlink:to="loc_us-gaap_CommonStockMember_019ff2d2-7625-7472-be27-84bf25c48e2a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_CommonStockAmountMember_019ff2d2-7625-7d63-942d-11c3e8718f50" xlink:href="irdm-20260930.xsd#irdm_CommonStockAmountMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ff2d2-7625-7517-a394-02f90834d395" xlink:to="loc_irdm_CommonStockAmountMember_019ff2d2-7625-7d63-942d-11c3e8718f50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019ff2d2-7625-7f96-a9b2-5a529a610b9c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ff2d2-7625-7517-a394-02f90834d395" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019ff2d2-7625-7f96-a9b2-5a529a610b9c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019ff2d2-7625-7ae7-9f2e-51d30b2fb81e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ff2d2-7625-7517-a394-02f90834d395" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019ff2d2-7625-7ae7-9f2e-51d30b2fb81e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019ff2d2-7625-7f3d-89a1-769ecd911d12" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019ff2d2-7625-7517-a394-02f90834d395" xlink:to="loc_us-gaap_RetainedEarningsMember_019ff2d2-7625-7f3d-89a1-769ecd911d12" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_019ff2d2-7625-77b7-b62c-6087793691fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_us-gaap_SharesOutstanding_019ff2d2-7625-77b7-b62c-6087793691fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross_019ff2d2-7625-7edc-a0a6-4e33885e6479" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesShareBasedCompensationGross_019ff2d2-7625-7edc-a0a6-4e33885e6479" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_019ff2d2-7625-74a0-b9db-f234bbae8521" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_019ff2d2-7625-74a0-b9db-f234bbae8521" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_019ff2d2-7625-7ad2-bf2e-2190f4136704" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodShares_019ff2d2-7625-7ad2-bf2e-2190f4136704" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesOutstanding_019ff2d2-7625-70b0-9d76-fa02cb0b8bfe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ff2d2-7625-76ea-8e28-a2152589b268" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_us-gaap_StockholdersEquity_019ff2d2-7625-76ea-8e28-a2152589b268" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019ff2d2-7625-7180-aea1-e638438475b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019ff2d2-7625-7180-aea1-e638438475b4" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensationGross_019ff2d2-7625-7cd8-8813-93938dc1a7d6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockIssuedDuringPeriodValueShareBasedCompensationGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueShareBasedCompensationGross_019ff2d2-7625-7cd8-8813-93938dc1a7d6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_AdjustmentsToAdditionalPaidInCapitalStockWithheldToCoverEmployeeTaxes_019ff2d2-7625-7f0a-9f86-68785bf95852" xlink:href="irdm-20260930.xsd#irdm_AdjustmentsToAdditionalPaidInCapitalStockWithheldToCoverEmployeeTaxes"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_irdm_AdjustmentsToAdditionalPaidInCapitalStockWithheldToCoverEmployeeTaxes_019ff2d2-7625-7f0a-9f86-68785bf95852" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_019ff2d2-7625-7140-af4f-882533a3f5b5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockRepurchasedAndRetiredDuringPeriodValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_us-gaap_StockRepurchasedAndRetiredDuringPeriodValue_019ff2d2-7625-7140-af4f-882533a3f5b5" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings_019ff2d2-7625-7149-9b47-5699a3529c1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalDividendsInExcessOfRetainedEarnings_019ff2d2-7625-7149-9b47-5699a3529c1c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_019ff2d2-7625-76db-8e0f-453949403b5c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_us-gaap_OtherComprehensiveIncomeForeignCurrencyTransactionAndTranslationAdjustmentNetOfTaxPortionAttributableToParent_019ff2d2-7625-76db-8e0f-453949403b5c" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_UnrealizedGainLossOnCashFlowHedgesNetOfTax_019ff2d2-7625-7ae6-9ae6-a4560f6f6074" xlink:href="irdm-20260930.xsd#irdm_UnrealizedGainLossOnCashFlowHedgesNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_irdm_UnrealizedGainLossOnCashFlowHedgesNetOfTax_019ff2d2-7625-7ae6-9ae6-a4560f6f6074" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019ff2d2-7625-7d76-ab8a-a7cf78f38521" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7d3f-b9aa-57497343c87b" xlink:to="loc_us-gaap_NetIncomeLoss_019ff2d2-7625-7d76-ab8a-a7cf78f38521" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019ff2d2-7625-7ba7-b13f-4edae3bc4ace" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="simple" xlink:href="irdm-20260930.xsd#CondensedConsolidatedStatementsofCashFlows"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/CondensedConsolidatedStatementsofCashFlows" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019ff2d2-7625-7035-adf2-ceab2335a491" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019ff2d2-7625-7397-a907-cc8b5ccd795a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7035-adf2-ceab2335a491" xlink:to="loc_us-gaap_StatementTable_019ff2d2-7625-7397-a907-cc8b5ccd795a" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsAxis_019ff2d2-7625-7c5b-83bb-f5252637ed34" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019ff2d2-7625-7397-a907-cc8b5ccd795a" xlink:to="loc_us-gaap_DividendsAxis_019ff2d2-7625-7c5b-83bb-f5252637ed34" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_019ff2d2-7625-7c5b-83bb-f5252637ed34_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DividendsAxis_019ff2d2-7625-7c5b-83bb-f5252637ed34" xlink:to="loc_us-gaap_DividendsDomain_019ff2d2-7625-7c5b-83bb-f5252637ed34_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_019ff2d2-7625-7fb1-bf96-9d60a0f17b30" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DividendsAxis_019ff2d2-7625-7c5b-83bb-f5252637ed34" xlink:to="loc_us-gaap_DividendsDomain_019ff2d2-7625-7fb1-bf96-9d60a0f17b30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7035-adf2-ceab2335a491" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019ff2d2-7625-7051-b405-633fe44732bc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_NetIncomeLoss_019ff2d2-7625-7051-b405-633fe44732bc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_019ff2d2-7625-7c51-9844-18e99b20df9f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DeferredIncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_DeferredIncomeTaxExpenseBenefit_019ff2d2-7625-7c51-9844-18e99b20df9f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_019ff2d2-7625-7676-8d30-ef58ddbeee44" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DepreciationDepletionAndAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_019ff2d2-7625-7676-8d30-ef58ddbeee44" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_AccretionOfSellerLoanDiscount_01a14b25-89cd-76b8-998a-f1647dff8d0b" xlink:href="irdm-20260930.xsd#irdm_AccretionOfSellerLoanDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_irdm_AccretionOfSellerLoanDiscount_01a14b25-89cd-76b8-998a-f1647dff8d0b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019ff2d2-7625-7b6c-b103-82d5c3eb9a27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_ShareBasedCompensation_019ff2d2-7625-7b6c-b103-82d5c3eb9a27" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfFinancingCosts_019ff2d2-7625-78f9-aaf0-1f11d2d0e2da" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AmortizationOfFinancingCosts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_AmortizationOfFinancingCosts_019ff2d2-7625-78f9-aaf0-1f11d2d0e2da" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019ff2d2-7625-7e42-8390-78d67833e528" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeLossFromEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_IncomeLossFromEquityMethodInvestments_019ff2d2-7625-7e42-8390-78d67833e528" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherOperatingActivitiesCashFlowStatement_019ff2d2-7625-7519-8a85-01d6718bc7dc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherOperatingActivitiesCashFlowStatement"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_OtherOperatingActivitiesCashFlowStatement_019ff2d2-7625-7519-8a85-01d6718bc7dc" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_019ff2d2-7625-71dd-a4a7-d292fa94817d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsReceivable_019ff2d2-7625-71dd-a4a7-d292fa94817d" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInInventories_019ff2d2-7625-70b4-afab-b73c0fa4493c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInInventories"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_IncreaseDecreaseInInventories_019ff2d2-7625-70b4-afab-b73c0fa4493c" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_019ff2d2-7625-7bb9-8481-e940392c28b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_IncreaseDecreaseInPrepaidDeferredExpenseAndOtherAssets_019ff2d2-7625-7bb9-8481-e940392c28b0" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_019ff2d2-7625-7b80-9665-4ef34003dee1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentAssets_019ff2d2-7625-7b80-9665-4ef34003dee1" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019ff2d2-7625-7d96-807b-bcec8172d55a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccountsPayable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_IncreaseDecreaseInAccountsPayable_019ff2d2-7625-7d96-807b-bcec8172d55a" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities_019ff2d2-7625-70e6-a8bb-00789f147edd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_IncreaseDecreaseInAccruedLiabilitiesAndOtherOperatingLiabilities_019ff2d2-7625-70e6-a8bb-00789f147edd" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInDeferredRevenue_019ff2d2-7625-761c-9e22-27febf17db86" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInDeferredRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_IncreaseDecreaseInDeferredRevenue_019ff2d2-7625-761c-9e22-27febf17db86" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities_019ff2d2-7625-71ab-ba88-8d4ca8c46204" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_IncreaseDecreaseInOtherNoncurrentLiabilities_019ff2d2-7625-71ab-ba88-8d4ca8c46204" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019ff2d2-7625-7b82-8cc3-7cd6a6fce226" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInOperatingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInOperatingActivitiesContinuingOperationsAbstract_019ff2d2-7625-79dc-9e49-696e73117e5a" xlink:to="loc_us-gaap_NetCashProvidedByUsedInOperatingActivities_019ff2d2-7625-7b82-8cc3-7cd6a6fce226" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_019ff2d2-7625-7b60-adc8-0e87cd16be7e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7035-adf2-ceab2335a491" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_019ff2d2-7625-7b60-adc8-0e87cd16be7e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019ff2d2-7625-7247-af41-ecb1cc2f7c0c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquirePropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_019ff2d2-7625-7b60-adc8-0e87cd16be7e" xlink:to="loc_us-gaap_PaymentsToAcquirePropertyPlantAndEquipment_019ff2d2-7625-7247-af41-ecb1cc2f7c0c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019ff2d2-7625-7d08-8852-1dcaa6d386d9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInInvestingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInInvestingActivitiesContinuingOperationsAbstract_019ff2d2-7625-7b60-adc8-0e87cd16be7e" xlink:to="loc_us-gaap_NetCashProvidedByUsedInInvestingActivities_019ff2d2-7625-7d08-8852-1dcaa6d386d9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_019ff2d2-7625-75bc-abfa-771c7cae598b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7035-adf2-ceab2335a491" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_019ff2d2-7625-75bc-abfa-771c7cae598b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInThreeMonthsOrLess_019ff2d2-7625-724f-8cbf-890ee2071fea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInThreeMonthsOrLess"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_019ff2d2-7625-75bc-abfa-771c7cae598b" xlink:to="loc_us-gaap_ProceedsFromRepaymentsOfShortTermDebtMaturingInThreeMonthsOrLess_019ff2d2-7625-724f-8cbf-890ee2071fea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_019ff2d2-7625-7e3d-8c90-61e8b0fc2e33" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_019ff2d2-7625-75bc-abfa-771c7cae598b" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_019ff2d2-7625-7e3d-8c90-61e8b0fc2e33" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_019ff2d2-7625-7089-8e33-741bc0ff78a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForRepurchaseOfCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_019ff2d2-7625-75bc-abfa-771c7cae598b" xlink:to="loc_us-gaap_PaymentsForRepurchaseOfCommonStock_019ff2d2-7625-7089-8e33-741bc0ff78a6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromStockOptionsExercised_019ff2d2-7625-79b2-96a6-57e51a9fbd98" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_019ff2d2-7625-75bc-abfa-771c7cae598b" xlink:to="loc_us-gaap_ProceedsFromStockOptionsExercised_019ff2d2-7625-79b2-96a6-57e51a9fbd98" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_019ff2d2-7625-7e7d-a659-5e5aa2ce1836" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_019ff2d2-7625-75bc-abfa-771c7cae598b" xlink:to="loc_us-gaap_PaymentsRelatedToTaxWithholdingForShareBasedCompensation_019ff2d2-7625-7e7d-a659-5e5aa2ce1836" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividendsCommonStock_019ff2d2-7625-796d-b1f5-3fcc8e064bdc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_019ff2d2-7625-75bc-abfa-771c7cae598b" xlink:to="loc_us-gaap_PaymentsOfDividendsCommonStock_019ff2d2-7625-796d-b1f5-3fcc8e064bdc" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019ff2d2-7625-7f97-92b2-a24178e4f8a3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetCashProvidedByUsedInFinancingActivities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetCashProvidedByUsedInFinancingActivitiesContinuingOperationsAbstract_019ff2d2-7625-75bc-abfa-771c7cae598b" xlink:to="loc_us-gaap_NetCashProvidedByUsedInFinancingActivities_019ff2d2-7625-7f97-92b2-a24178e4f8a3" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019ff2d2-7625-74ae-a509-3d543640791a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7035-adf2-ceab2335a491" xlink:to="loc_us-gaap_EffectOfExchangeRateOnCashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019ff2d2-7625-74ae-a509-3d543640791a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019ff2d2-7625-72d3-a5d7-5443d104f5b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7035-adf2-ceab2335a491" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalentsPeriodIncreaseDecreaseIncludingExchangeRateEffect_019ff2d2-7625-72d3-a5d7-5443d104f5b4" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019ff2d2-7625-7008-b340-537f550fbb2a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7035-adf2-ceab2335a491" xlink:to="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019ff2d2-7625-7008-b340-537f550fbb2a" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents_019ff2d2-7625-7cf6-ad3c-1ade7d65eed4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashCashEquivalentsRestrictedCashAndRestrictedCashEquivalents"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SupplementalCashFlowInformationAbstract_019ff2d2-7625-7fe3-8a8a-ab7b1d5da688" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SupplementalCashFlowInformationAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7035-adf2-ceab2335a491" xlink:to="loc_us-gaap_SupplementalCashFlowInformationAbstract_019ff2d2-7625-7fe3-8a8a-ab7b1d5da688" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaidNet_019ff2d2-7625-7d59-bb2c-34639fd8a1cb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_019ff2d2-7625-7fe3-8a8a-ab7b1d5da688" xlink:to="loc_us-gaap_InterestPaidNet_019ff2d2-7625-7d59-bb2c-34639fd8a1cb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxesPaidNet_019ff2d2-7625-7594-aa07-712ae8af0ed3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IncomeTaxesPaidNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SupplementalCashFlowInformationAbstract_019ff2d2-7625-7fe3-8a8a-ab7b1d5da688" xlink:to="loc_us-gaap_IncomeTaxesPaidNet_019ff2d2-7625-7594-aa07-712ae8af0ed3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019ff2d2-7625-7e0d-9487-b3f0c5eb74f3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7035-adf2-ceab2335a491" xlink:to="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019ff2d2-7625-7e0d-9487-b3f0c5eb74f3" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_019ff2d2-7625-7313-9399-d757b2d483ac" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CapitalExpendituresIncurredButNotYetPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019ff2d2-7625-7e0d-9487-b3f0c5eb74f3" xlink:to="loc_us-gaap_CapitalExpendituresIncurredButNotYetPaid_019ff2d2-7625-7313-9399-d757b2d483ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_019ff2d2-7625-7b25-8add-c6d833e62fcd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019ff2d2-7625-7e0d-9487-b3f0c5eb74f3" xlink:to="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_019ff2d2-7625-7b25-8add-c6d833e62fcd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount_019ff2d2-7625-72a4-a9f6-b7f5d040aa56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashFlowNoncashInvestingAndFinancingActivitiesDisclosureAbstract_019ff2d2-7625-7e0d-9487-b3f0c5eb74f3" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsCapitalizedAmount_019ff2d2-7625-72a4-a9f6-b7f5d040aa56" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_01a14b48-2446-779f-998f-8c70aeff0134" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsToAcquireEquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7035-adf2-ceab2335a491" xlink:to="loc_us-gaap_PaymentsToAcquireEquityMethodInvestments_01a14b48-2446-779f-998f-8c70aeff0134" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfUnsecuredDebt_01a14b4c-d75c-73e2-99ea-a18c99c43b5d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RepaymentsOfUnsecuredDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019ff2d2-7625-7035-adf2-ceab2335a491" xlink:to="loc_us-gaap_RepaymentsOfUnsecuredDebt_01a14b4c-d75c-73e2-99ea-a18c99c43b5d" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/SignificantAccountingPoliciesScheduleofInventoryDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#SignificantAccountingPoliciesScheduleofInventoryDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/SignificantAccountingPoliciesScheduleofInventoryDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_01a14b2d-a0f8-7dce-8717-fb9dba2d4d7b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_01a14b2d-a0f8-74b1-9ea8-1c9698b3622e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_01a14b2d-a0f8-7dce-8717-fb9dba2d4d7b" xlink:to="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_01a14b2d-a0f8-74b1-9ea8-1c9698b3622e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a14b2d-a0f8-7a2d-86d1-949f2dc9e6a0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_01a14b2d-a0f8-74b1-9ea8-1c9698b3622e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a14b2d-a0f8-7a2d-86d1-949f2dc9e6a0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a14b2d-a0f8-7a2d-86d1-949f2dc9e6a0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a14b2d-a0f8-7a2d-86d1-949f2dc9e6a0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a14b2d-a0f8-7a2d-86d1-949f2dc9e6a0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a14b2d-a0f8-7c95-bfd2-85a0f2923e0b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a14b2d-a0f8-7a2d-86d1-949f2dc9e6a0" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a14b2d-a0f8-7c95-bfd2-85a0f2923e0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_01a14b2d-a0f8-7c2d-a6c3-315dc036ddf5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a14b2d-a0f8-7c95-bfd2-85a0f2923e0b" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_01a14b2d-a0f8-7c2d-a6c3-315dc036ddf5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_01a14b30-526f-72c5-ba40-fd88053182c0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a14b2d-a0f8-7c95-bfd2-85a0f2923e0b" xlink:to="loc_us-gaap_TradeNamesMember_01a14b30-526f-72c5-ba40-fd88053182c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_01a14b2d-a0f8-7fa0-9355-acb6fbfadfd5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_01a14b2d-a0f8-7dce-8717-fb9dba2d4d7b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_01a14b2d-a0f8-7fa0-9355-acb6fbfadfd5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_01a14b2e-b97e-7fc9-be0c-1b62414bae24" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_01a14b2d-a0f8-7dce-8717-fb9dba2d4d7b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_01a14b2e-b97e-7fc9-be0c-1b62414bae24" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_01a14b2f-1ff7-7dd8-a4c8-5b5e7476a638" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassLineItems_01a14b2d-a0f8-7dce-8717-fb9dba2d4d7b" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_01a14b2f-1ff7-7dd8-a4c8-5b5e7476a638" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/CashandCashEquivalentsRestrictedCashandMarketableSecuritiesDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#CashandCashEquivalentsRestrictedCashandMarketableSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/CashandCashEquivalentsRestrictedCashandMarketableSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsLineItems_019ff2d2-7625-7025-bd2e-bc55257374d1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019ff2d2-7625-7de8-92ff-e9374537a98e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfCashAndCashEquivalentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019ff2d2-7625-7025-bd2e-bc55257374d1" xlink:to="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019ff2d2-7625-7de8-92ff-e9374537a98e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAxis_019ff2d2-7625-7718-aa24-c181485c367c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019ff2d2-7625-7de8-92ff-e9374537a98e" xlink:to="loc_us-gaap_CashAndCashEquivalentsAxis_019ff2d2-7625-7718-aa24-c181485c367c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ff2d2-7625-7718-aa24-c181485c367c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019ff2d2-7625-7718-aa24-c181485c367c" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ff2d2-7625-7718-aa24-c181485c367c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ff2d2-7625-71e6-964f-20cb197188b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CashAndCashEquivalentsAxis_019ff2d2-7625-7718-aa24-c181485c367c" xlink:to="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ff2d2-7625-71e6-964f-20cb197188b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashMember_019ff2d2-7625-7e1e-94f8-8399f5369006" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ff2d2-7625-71e6-964f-20cb197188b0" xlink:to="loc_us-gaap_CashMember_019ff2d2-7625-7e1e-94f8-8399f5369006" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsMember_019ff2d2-7625-79c2-be03-9a5ac7db7d2e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RestrictedCashAndCashEquivalentsCashAndCashEquivalentsMember_019ff2d2-7625-71e6-964f-20cb197188b0" xlink:to="loc_us-gaap_MoneyMarketFundsMember_019ff2d2-7625-79c2-be03-9a5ac7db7d2e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ff2d2-7625-799e-a9e7-8e2cc0cdb173" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfCashAndCashEquivalentsTable_019ff2d2-7625-7de8-92ff-e9374537a98e" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ff2d2-7625-799e-a9e7-8e2cc0cdb173" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ff2d2-7625-799e-a9e7-8e2cc0cdb173_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ff2d2-7625-799e-a9e7-8e2cc0cdb173" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ff2d2-7625-799e-a9e7-8e2cc0cdb173_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ff2d2-7625-745d-94cd-2dc07d87668d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019ff2d2-7625-799e-a9e7-8e2cc0cdb173" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ff2d2-7625-745d-94cd-2dc07d87668d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019ff2d2-7625-744b-a5fc-2d66000fe525" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019ff2d2-7625-745d-94cd-2dc07d87668d" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019ff2d2-7625-744b-a5fc-2d66000fe525" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Cash_019ff2d2-7625-77c8-902b-9d58c6d2753c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Cash"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019ff2d2-7625-7025-bd2e-bc55257374d1" xlink:to="loc_us-gaap_Cash_019ff2d2-7625-77c8-902b-9d58c6d2753c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MoneyMarketFundsAtCarryingValue_019ff2d2-7625-7a72-ae35-c98868278b49" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_MoneyMarketFundsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019ff2d2-7625-7025-bd2e-bc55257374d1" xlink:to="loc_us-gaap_MoneyMarketFundsAtCarryingValue_019ff2d2-7625-7a72-ae35-c98868278b49" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019ff2d2-7625-778a-acd5-7cac85bd8b5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CashAndCashEquivalentsAtCarryingValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CashAndCashEquivalentsLineItems_019ff2d2-7625-7025-bd2e-bc55257374d1" xlink:to="loc_us-gaap_CashAndCashEquivalentsAtCarryingValue_019ff2d2-7625-778a-acd5-7cac85bd8b5b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/IntangibleAssetsGoodwillandOtherDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#IntangibleAssetsGoodwillandOtherDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/IntangibleAssetsGoodwillandOtherDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ff2d2-7625-7068-a693-67c97f6ffef8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_019ff2d2-7625-7d17-b5e8-b5db660dc092" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ff2d2-7625-7068-a693-67c97f6ffef8" xlink:to="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_019ff2d2-7625-7d17-b5e8-b5db660dc092" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019ff2d2-7625-7cf7-8ff9-bbc6aea06694" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_019ff2d2-7625-7d17-b5e8-b5db660dc092" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019ff2d2-7625-7cf7-8ff9-bbc6aea06694" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ff2d2-7625-7cf7-8ff9-bbc6aea06694_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019ff2d2-7625-7cf7-8ff9-bbc6aea06694" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ff2d2-7625-7cf7-8ff9-bbc6aea06694_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ff2d2-7625-7229-bc38-63eb5914069c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019ff2d2-7625-7cf7-8ff9-bbc6aea06694" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ff2d2-7625-7229-bc38-63eb5914069c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_019ff2d2-7625-77e7-b5fe-aaa18aca6cb7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ff2d2-7625-7229-bc38-63eb5914069c" xlink:to="loc_us-gaap_TradeNamesMember_019ff2d2-7625-77e7-b5fe-aaa18aca6cb7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LicensingAgreementsMember_019ff2d2-7625-7259-a2d2-8b5181f99215" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LicensingAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019ff2d2-7625-7229-bc38-63eb5914069c" xlink:to="loc_us-gaap_LicensingAgreementsMember_019ff2d2-7625-7259-a2d2-8b5181f99215" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ff2d2-7625-719d-ac4b-62c3b5fefac9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_019ff2d2-7625-7d17-b5e8-b5db660dc092" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ff2d2-7625-719d-ac4b-62c3b5fefac9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ff2d2-7625-719d-ac4b-62c3b5fefac9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ff2d2-7625-719d-ac4b-62c3b5fefac9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ff2d2-7625-719d-ac4b-62c3b5fefac9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ff2d2-7625-7715-9337-0eb2d62ad816" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019ff2d2-7625-719d-ac4b-62c3b5fefac9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ff2d2-7625-7715-9337-0eb2d62ad816" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntellectualPropertyMember_019ff2d2-7625-79d9-b0bb-bb0d25218d41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntellectualPropertyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ff2d2-7625-7715-9337-0eb2d62ad816" xlink:to="loc_us-gaap_IntellectualPropertyMember_019ff2d2-7625-79d9-b0bb-bb0d25218d41" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PatentsMember_019ff2d2-7625-72b7-aa13-f153281f10c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PatentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ff2d2-7625-7715-9337-0eb2d62ad816" xlink:to="loc_us-gaap_PatentsMember_019ff2d2-7625-72b7-aa13-f153281f10c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019ff2d2-7625-7084-beb2-5fcd93078452" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019ff2d2-7625-7715-9337-0eb2d62ad816" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019ff2d2-7625-7084-beb2-5fcd93078452" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ff2d2-7625-7693-85e6-1eb1762bd1c7" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfIndefiniteLivedIntangibleAssetsTable_019ff2d2-7625-7d17-b5e8-b5db660dc092" xlink:to="loc_srt_RangeAxis_019ff2d2-7625-7693-85e6-1eb1762bd1c7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ff2d2-7625-7693-85e6-1eb1762bd1c7_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ff2d2-7625-7693-85e6-1eb1762bd1c7" xlink:to="loc_srt_RangeMember_019ff2d2-7625-7693-85e6-1eb1762bd1c7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ff2d2-7625-779f-b261-dcc1be7a3b19" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ff2d2-7625-7693-85e6-1eb1762bd1c7" xlink:to="loc_srt_RangeMember_019ff2d2-7625-779f-b261-dcc1be7a3b19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019ff2d2-7625-70fa-affb-7a4d02e6a935" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ff2d2-7625-779f-b261-dcc1be7a3b19" xlink:to="loc_srt_MinimumMember_019ff2d2-7625-70fa-affb-7a4d02e6a935" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019ff2d2-7625-7392-90a5-7a3863ec4f13" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ff2d2-7625-779f-b261-dcc1be7a3b19" xlink:to="loc_srt_MaximumMember_019ff2d2-7625-7392-90a5-7a3863ec4f13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019ff2d2-7625-7232-b980-9fae42085261" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ff2d2-7625-7068-a693-67c97f6ffef8" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019ff2d2-7625-7232-b980-9fae42085261" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019ff2d2-7625-72ac-96e0-e33d424b6fa5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ff2d2-7625-7068-a693-67c97f6ffef8" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019ff2d2-7625-72ac-96e0-e33d424b6fa5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019ff2d2-7625-7caf-a8fd-de476d53d993" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ff2d2-7625-7068-a693-67c97f6ffef8" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019ff2d2-7625-7caf-a8fd-de476d53d993" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019ff2d2-7625-7687-affe-f2ca19f205ea" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ff2d2-7625-7068-a693-67c97f6ffef8" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019ff2d2-7625-7687-affe-f2ca19f205ea" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_019ff2d2-7625-7fd2-82c4-793f7cdca8fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ff2d2-7625-7068-a693-67c97f6ffef8" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_019ff2d2-7625-7fd2-82c4-793f7cdca8fc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019ff2d2-7625-79a4-a00d-8034dfccb2b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsLineItems_019ff2d2-7625-7068-a693-67c97f6ffef8" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019ff2d2-7625-79a4-a00d-8034dfccb2b0" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/DebtNarrativeDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#DebtNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/DebtNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityTable_019ff2d2-7625-7b2e-b7f5-7c59fe980f27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LineOfCreditFacilityTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_us-gaap_LineOfCreditFacilityTable_019ff2d2-7625-7b2e-b7f5-7c59fe980f27" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019ff2d2-7625-79ce-bbaa-d43aee9a287a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ff2d2-7625-7b2e-b7f5-7c59fe980f27" xlink:to="loc_us-gaap_VariableRateAxis_019ff2d2-7625-79ce-bbaa-d43aee9a287a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019ff2d2-7625-79ce-bbaa-d43aee9a287a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_019ff2d2-7625-79ce-bbaa-d43aee9a287a" xlink:to="loc_us-gaap_VariableRateDomain_019ff2d2-7625-79ce-bbaa-d43aee9a287a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019ff2d2-7625-7f61-8704-8131911075b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_019ff2d2-7625-79ce-bbaa-d43aee9a287a" xlink:to="loc_us-gaap_VariableRateDomain_019ff2d2-7625-7f61-8704-8131911075b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateFloorMember_019ff2d2-7625-7b77-b544-0469ee01d1a1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateFloorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019ff2d2-7625-7f61-8704-8131911075b0" xlink:to="loc_us-gaap_InterestRateFloorMember_019ff2d2-7625-7b77-b544-0469ee01d1a1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCapMember_019ff2d2-7625-7240-ae5e-e1a0bbff5201" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateCapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019ff2d2-7625-7f61-8704-8131911075b0" xlink:to="loc_us-gaap_InterestRateCapMember_019ff2d2-7625-7240-ae5e-e1a0bbff5201" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_019ff2d2-7625-7a4f-9c7b-af131791a460" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019ff2d2-7625-7f61-8704-8131911075b0" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_019ff2d2-7625-7a4f-9c7b-af131791a460" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ff2d2-7625-7926-8c32-62fe4e814c0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ff2d2-7625-7b2e-b7f5-7c59fe980f27" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ff2d2-7625-7926-8c32-62fe4e814c0a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ff2d2-7625-7926-8c32-62fe4e814c0a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ff2d2-7625-7926-8c32-62fe4e814c0a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ff2d2-7625-7926-8c32-62fe4e814c0a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ff2d2-7625-73e9-ac7a-43652d46e2a6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ff2d2-7625-7926-8c32-62fe4e814c0a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ff2d2-7625-73e9-ac7a-43652d46e2a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019ff2d2-7625-737e-9c84-6dfddbdb201e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ff2d2-7625-73e9-ac7a-43652d46e2a6" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019ff2d2-7625-737e-9c84-6dfddbdb201e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_TermLoanBRefinancedMember_019ff2d2-7625-7942-b7ae-3da7876417af" xlink:href="irdm-20260930.xsd#irdm_TermLoanBRefinancedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ff2d2-7625-73e9-ac7a-43652d46e2a6" xlink:to="loc_irdm_TermLoanBRefinancedMember_019ff2d2-7625-7942-b7ae-3da7876417af" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ff2d2-7625-76da-a672-00c79f9e920f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LineOfCreditFacilityTable_019ff2d2-7625-7b2e-b7f5-7c59fe980f27" xlink:to="loc_srt_RangeAxis_019ff2d2-7625-76da-a672-00c79f9e920f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ff2d2-7625-76da-a672-00c79f9e920f_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ff2d2-7625-76da-a672-00c79f9e920f" xlink:to="loc_srt_RangeMember_019ff2d2-7625-76da-a672-00c79f9e920f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ff2d2-7625-7433-95d6-d7f3ce64718e" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ff2d2-7625-76da-a672-00c79f9e920f" xlink:to="loc_srt_RangeMember_019ff2d2-7625-7433-95d6-d7f3ce64718e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019ff2d2-7625-7200-84c8-c7b7f1ecc5cf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ff2d2-7625-7433-95d6-d7f3ce64718e" xlink:to="loc_srt_MinimumMember_019ff2d2-7625-7200-84c8-c7b7f1ecc5cf" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019ff2d2-7625-7537-bce5-9c50e3d94d79" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019ff2d2-7625-7537-bce5-9c50e3d94d79" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_DiscountOnDebtIssuance_019ff2d2-7625-7c07-9991-99c19a0fb355" xlink:href="irdm-20260930.xsd#irdm_DiscountOnDebtIssuance"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_irdm_DiscountOnDebtIssuance_019ff2d2-7625-7c07-9991-99c19a0fb355" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromIssuanceOfDebt_019ff2d2-7625-7966-b3b8-9f0e359e3a1a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ProceedsFromIssuanceOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_us-gaap_ProceedsFromIssuanceOfDebt_019ff2d2-7625-7966-b3b8-9f0e359e3a1a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019ff2d2-7625-74db-bed1-9cc60a3090fc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019ff2d2-7625-74db-bed1-9cc60a3090fc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019ff2d2-7625-78d2-bdc9-ce458a3d8136" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019ff2d2-7625-78d2-bdc9-ce458a3d8136" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPaymentPrincipal_019ff2d2-7625-77bb-8beb-76a2fc70894e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentPeriodicPaymentPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPaymentPrincipal_019ff2d2-7625-77bb-8beb-76a2fc70894e" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFee_019ff2d2-7625-7d21-ad9b-d9cd30995141" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentFee"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_us-gaap_DebtInstrumentFee_019ff2d2-7625-7d21-ad9b-d9cd30995141" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_019ff2d2-7625-7fa3-8ed3-6359cf0c7eb6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscountPremiumAndDebtIssuanceCostsNet_019ff2d2-7625-7fa3-8ed3-6359cf0c7eb6" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019ff2d2-7625-745c-8c5c-68335587a141" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_us-gaap_LongTermDebt_019ff2d2-7625-745c-8c5c-68335587a141" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebtFairValue_019ff2d2-7625-7927-a93a-939b28aae635" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongTermDebtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_us-gaap_LongTermDebtFairValue_019ff2d2-7625-7927-a93a-939b28aae635" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_ExcessCashFlowPrepayment_019ff2d2-7625-75c1-96ee-da597d65f136" xlink:href="irdm-20260930.xsd#irdm_ExcessCashFlowPrepayment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_irdm_ExcessCashFlowPrepayment_019ff2d2-7625-75c1-96ee-da597d65f136" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RatioOfIndebtednessToNetCapital1_019ff2d2-7625-73ac-8359-6633e348535f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RatioOfIndebtednessToNetCapital1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_us-gaap_RatioOfIndebtednessToNetCapital1_019ff2d2-7625-73ac-8359-6633e348535f" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_CreditFacilityDrawdownFloorforApplicationofFirstLienNetLeverageRatio_019ff2d2-7625-768e-b0d2-4318111084a9" xlink:href="irdm-20260930.xsd#irdm_CreditFacilityDrawdownFloorforApplicationofFirstLienNetLeverageRatio"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_irdm_CreditFacilityDrawdownFloorforApplicationofFirstLienNetLeverageRatio_019ff2d2-7625-768e-b0d2-4318111084a9" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPayableCurrentAndNoncurrent_019ff2d2-7625-75b0-9ae4-f6f215504ac7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LineOfCreditFacilityLineItems_019ff2d2-7625-7b13-a46c-bf6bbd5cc50b" xlink:to="loc_us-gaap_InterestPayableCurrentAndNoncurrent_019ff2d2-7625-75b0-9ae4-f6f215504ac7" xlink:type="arc" order="13"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/DerivativesDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#DerivativesDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/DerivativesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeLineItems_019ff2d2-7625-7548-8649-e30ca29d74e6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeTable_019ff2d2-7625-7187-9cee-282eec989786" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DerivativeLineItems_019ff2d2-7625-7548-8649-e30ca29d74e6" xlink:to="loc_us-gaap_DerivativeTable_019ff2d2-7625-7187-9cee-282eec989786" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019ff2d2-7625-7c8a-bb2e-7a6177d68284" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019ff2d2-7625-7187-9cee-282eec989786" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019ff2d2-7625-7c8a-bb2e-7a6177d68284" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019ff2d2-7625-7c8a-bb2e-7a6177d68284_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019ff2d2-7625-7c8a-bb2e-7a6177d68284" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019ff2d2-7625-7c8a-bb2e-7a6177d68284_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019ff2d2-7625-7aae-b5d0-d23df713b84e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019ff2d2-7625-7c8a-bb2e-7a6177d68284" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019ff2d2-7625-7aae-b5d0-d23df713b84e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCapMember_019ff2d2-7625-7381-9b51-6c5e49fd3e15" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateCapMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019ff2d2-7625-7aae-b5d0-d23df713b84e" xlink:to="loc_us-gaap_InterestRateCapMember_019ff2d2-7625-7381-9b51-6c5e49fd3e15" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019ff2d2-7625-7eae-9d7f-9a00e69cd66b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019ff2d2-7625-7187-9cee-282eec989786" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019ff2d2-7625-7eae-9d7f-9a00e69cd66b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ff2d2-7625-7eae-9d7f-9a00e69cd66b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ff2d2-7625-7eae-9d7f-9a00e69cd66b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ff2d2-7625-7eae-9d7f-9a00e69cd66b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019ff2d2-7625-7d43-b0ba-154bbad29e8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019ff2d2-7625-7eae-9d7f-9a00e69cd66b" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019ff2d2-7625-7d43-b0ba-154bbad29e8f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_TermLoanBRefinancedMember_019ff2d2-7625-72ef-8860-e3b6a01fd4b1" xlink:href="irdm-20260930.xsd#irdm_TermLoanBRefinancedMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019ff2d2-7625-7d43-b0ba-154bbad29e8f" xlink:to="loc_irdm_TermLoanBRefinancedMember_019ff2d2-7625-72ef-8860-e3b6a01fd4b1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019ff2d2-7625-7ecf-a750-2e84889e2897" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DerivativeTable_019ff2d2-7625-7187-9cee-282eec989786" xlink:to="loc_us-gaap_VariableRateAxis_019ff2d2-7625-7ecf-a750-2e84889e2897" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019ff2d2-7625-7ecf-a750-2e84889e2897_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_019ff2d2-7625-7ecf-a750-2e84889e2897" xlink:to="loc_us-gaap_VariableRateDomain_019ff2d2-7625-7ecf-a750-2e84889e2897_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019ff2d2-7625-721e-af4d-bebca34cafa6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_019ff2d2-7625-7ecf-a750-2e84889e2897" xlink:to="loc_us-gaap_VariableRateDomain_019ff2d2-7625-721e-af4d-bebca34cafa6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_019ff2d2-7625-759f-baeb-a94f4d384019" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019ff2d2-7625-721e-af4d-bebca34cafa6" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember_019ff2d2-7625-759f-baeb-a94f4d384019" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeCapInterestRate_019ff2d2-7625-70f7-aebd-6f2a88094739" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeCapInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019ff2d2-7625-7548-8649-e30ca29d74e6" xlink:to="loc_us-gaap_DerivativeCapInterestRate_019ff2d2-7625-70f7-aebd-6f2a88094739" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeFixedInterestRate_019ff2d2-7625-73dd-95dd-e1b672b64990" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeFixedInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019ff2d2-7625-7548-8649-e30ca29d74e6" xlink:to="loc_us-gaap_DerivativeFixedInterestRate_019ff2d2-7625-73dd-95dd-e1b672b64990" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeNotionalAmount_019ff2d2-7625-7bcf-9eef-527618f53b3c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeNotionalAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019ff2d2-7625-7548-8649-e30ca29d74e6" xlink:to="loc_us-gaap_DerivativeNotionalAmount_019ff2d2-7625-7bcf-9eef-527618f53b3c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCashFlowHedgeAssetAtFairValue_019ff2d2-7625-7d35-873e-6369de69d479" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateCashFlowHedgeAssetAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019ff2d2-7625-7548-8649-e30ca29d74e6" xlink:to="loc_us-gaap_InterestRateCashFlowHedgeAssetAtFairValue_019ff2d2-7625-7d35-873e-6369de69d479" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestRateCashFlowHedgeLiabilityAtFairValue_019ff2d2-7625-7438-a40e-19e2cdfb1806" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestRateCashFlowHedgeLiabilityAtFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019ff2d2-7625-7548-8649-e30ca29d74e6" xlink:to="loc_us-gaap_InterestRateCashFlowHedgeLiabilityAtFairValue_019ff2d2-7625-7438-a40e-19e2cdfb1806" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestCostsIncurred_019ff2d2-7625-7506-b7c0-faa2bb0ef721" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_InterestCostsIncurred"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019ff2d2-7625-7548-8649-e30ca29d74e6" xlink:to="loc_us-gaap_InterestCostsIncurred_019ff2d2-7625-7506-b7c0-faa2bb0ef721" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeGainOnDerivative_019ff2d2-7625-70cf-b977-48551aba5e00" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DerivativeGainOnDerivative"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeLineItems_019ff2d2-7625-7548-8649-e30ca29d74e6" xlink:to="loc_us-gaap_DerivativeGainOnDerivative_019ff2d2-7625-70cf-b977-48551aba5e00" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/EquityTransactionsDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#EquityTransactionsDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/EquityTransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockLineItems_019ff2d2-7625-71b5-b13b-77dad3d82113" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ClassOfStockLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfStockByClassTable_019ff2d2-7625-714a-847c-e0173105b409" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfStockByClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ClassOfStockLineItems_019ff2d2-7625-71b5-b13b-77dad3d82113" xlink:to="loc_us-gaap_ScheduleOfStockByClassTable_019ff2d2-7625-714a-847c-e0173105b409" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsAxis_019ff2d2-7625-7d05-b68f-28bc194fa97f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfStockByClassTable_019ff2d2-7625-714a-847c-e0173105b409" xlink:to="loc_us-gaap_DividendsAxis_019ff2d2-7625-7d05-b68f-28bc194fa97f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_019ff2d2-7625-7d05-b68f-28bc194fa97f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DividendsAxis_019ff2d2-7625-7d05-b68f-28bc194fa97f" xlink:to="loc_us-gaap_DividendsDomain_019ff2d2-7625-7d05-b68f-28bc194fa97f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsDomain_019ff2d2-7625-7a64-8930-2826c825ee64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DividendsAxis_019ff2d2-7625-7d05-b68f-28bc194fa97f" xlink:to="loc_us-gaap_DividendsDomain_019ff2d2-7625-7a64-8930-2826c825ee64" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_TotalAuthorizedPreferredStockNumber_019ff2d2-7625-7df9-be7e-7d01607c0cd1" xlink:href="irdm-20260930.xsd#irdm_TotalAuthorizedPreferredStockNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019ff2d2-7625-71b5-b13b-77dad3d82113" xlink:to="loc_irdm_TotalAuthorizedPreferredStockNumber_019ff2d2-7625-7df9-be7e-7d01607c0cd1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019ff2d2-7625-780a-87dd-893036b06e41" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockParOrStatedValuePerShare"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019ff2d2-7625-71b5-b13b-77dad3d82113" xlink:to="loc_us-gaap_PreferredStockParOrStatedValuePerShare_019ff2d2-7625-780a-87dd-893036b06e41" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesIssued_019ff2d2-7625-7955-a026-5121b54df95d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesIssued"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019ff2d2-7625-71b5-b13b-77dad3d82113" xlink:to="loc_us-gaap_PreferredStockSharesIssued_019ff2d2-7625-7955-a026-5121b54df95d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockShareSubscriptions_019ff2d2-7625-71c9-88e5-29cba199848c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockShareSubscriptions"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019ff2d2-7625-71b5-b13b-77dad3d82113" xlink:to="loc_us-gaap_PreferredStockShareSubscriptions_019ff2d2-7625-71c9-88e5-29cba199848c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PreferredStockSharesOutstanding_019ff2d2-7625-73f2-970a-ddc52eb33346" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PreferredStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019ff2d2-7625-71b5-b13b-77dad3d82113" xlink:to="loc_us-gaap_PreferredStockSharesOutstanding_019ff2d2-7625-73f2-970a-ddc52eb33346" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockDividendsPerShareDeclared_019ff2d2-7625-7bb7-9643-2f222ddce2b4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonStockDividendsPerShareDeclared"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019ff2d2-7625-71b5-b13b-77dad3d82113" xlink:to="loc_us-gaap_CommonStockDividendsPerShareDeclared_019ff2d2-7625-7bb7-9643-2f222ddce2b4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsOfDividendsCommonStock_019ff2d2-7625-7c5b-82ab-835300c1f29e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsOfDividendsCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019ff2d2-7625-71b5-b13b-77dad3d82113" xlink:to="loc_us-gaap_PaymentsOfDividendsCommonStock_019ff2d2-7625-7c5b-82ab-835300c1f29e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_019ff2d2-7625-7de9-bba4-3d9bea5d2092" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DividendsPayableCurrentAndNoncurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019ff2d2-7625-71b5-b13b-77dad3d82113" xlink:to="loc_us-gaap_DividendsPayableCurrentAndNoncurrent_019ff2d2-7625-7de9-bba4-3d9bea5d2092" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019ff2d2-7625-74ef-baa2-83b8aa478a7f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_StockRepurchaseProgramAuthorizedAmount1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockLineItems_019ff2d2-7625-71b5-b13b-77dad3d82113" xlink:to="loc_srt_StockRepurchaseProgramAuthorizedAmount1_019ff2d2-7625-74ef-baa2-83b8aa478a7f" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/RevenueSummaryofServiceRevenueDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#RevenueSummaryofServiceRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/RevenueSummaryofServiceRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019ff2d2-7625-702d-b893-dcfd47b1a9c6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019ff2d2-7625-7d20-b0e1-1fc99be231a8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ff2d2-7625-702d-b893-dcfd47b1a9c6" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019ff2d2-7625-7d20-b0e1-1fc99be231a8" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019ff2d2-7625-7aee-907b-0f6bc4d7a442" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ff2d2-7625-7d20-b0e1-1fc99be231a8" xlink:to="loc_srt_ProductOrServiceAxis_019ff2d2-7625-7aee-907b-0f6bc4d7a442" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7aee-907b-0f6bc4d7a442_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019ff2d2-7625-7aee-907b-0f6bc4d7a442" xlink:to="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7aee-907b-0f6bc4d7a442_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7732-bfa0-5e3d525ad57b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019ff2d2-7625-7aee-907b-0f6bc4d7a442" xlink:to="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7732-bfa0-5e3d525ad57b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_CommercialVoiceandDataServicesMember_019ff2d2-7625-7f02-b064-13d7ca19f3d7" xlink:href="irdm-20260930.xsd#irdm_CommercialVoiceandDataServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7732-bfa0-5e3d525ad57b" xlink:to="loc_irdm_CommercialVoiceandDataServicesMember_019ff2d2-7625-7f02-b064-13d7ca19f3d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_CommercialIoTDataServicesMember_019ff2d2-7625-75ae-a732-0666683c50e0" xlink:href="irdm-20260930.xsd#irdm_CommercialIoTDataServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7732-bfa0-5e3d525ad57b" xlink:to="loc_irdm_CommercialIoTDataServicesMember_019ff2d2-7625-75ae-a732-0666683c50e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_CommercialBroadbandServicesMember_019ff2d2-7625-7fc3-8619-76c5318104cb" xlink:href="irdm-20260930.xsd#irdm_CommercialBroadbandServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7732-bfa0-5e3d525ad57b" xlink:to="loc_irdm_CommercialBroadbandServicesMember_019ff2d2-7625-7fc3-8619-76c5318104cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_HostedPayloadandOtherDataServicesMember_019ff2d2-7625-71b3-a4d1-2aa9226c0916" xlink:href="irdm-20260930.xsd#irdm_HostedPayloadandOtherDataServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7732-bfa0-5e3d525ad57b" xlink:to="loc_irdm_HostedPayloadandOtherDataServicesMember_019ff2d2-7625-71b3-a4d1-2aa9226c0916" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceMember_019ff2d2-7625-7f6f-880a-84f03da38c46" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ServiceMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7732-bfa0-5e3d525ad57b" xlink:to="loc_us-gaap_ServiceMember_019ff2d2-7625-7f6f-880a-84f03da38c46" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_EngineeringandSupportServicesMember_019ff2d2-7625-7e28-938f-c0b2474774f4" xlink:href="irdm-20260930.xsd#irdm_EngineeringandSupportServicesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7732-bfa0-5e3d525ad57b" xlink:to="loc_irdm_EngineeringandSupportServicesMember_019ff2d2-7625-7e28-938f-c0b2474774f4" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019ff2d2-7625-7026-b062-96152bdaf04f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019ff2d2-7625-7d20-b0e1-1fc99be231a8" xlink:to="loc_srt_MajorCustomersAxis_019ff2d2-7625-7026-b062-96152bdaf04f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019ff2d2-7625-7026-b062-96152bdaf04f_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019ff2d2-7625-7026-b062-96152bdaf04f" xlink:to="loc_srt_NameOfMajorCustomerDomain_019ff2d2-7625-7026-b062-96152bdaf04f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019ff2d2-7625-7ded-b354-f53b8589ff79" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019ff2d2-7625-7026-b062-96152bdaf04f" xlink:to="loc_srt_NameOfMajorCustomerDomain_019ff2d2-7625-7ded-b354-f53b8589ff79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_CommercialMember_019ff2d2-7625-7060-bd13-5d02bf09af45" xlink:href="irdm-20260930.xsd#irdm_CommercialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019ff2d2-7625-7ded-b354-f53b8589ff79" xlink:to="loc_irdm_CommercialMember_019ff2d2-7625-7060-bd13-5d02bf09af45" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_USGovernmentMember_019ff2d2-7625-73fd-b508-01ece56e3001" xlink:href="irdm-20260930.xsd#irdm_USGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019ff2d2-7625-7ded-b354-f53b8589ff79" xlink:to="loc_irdm_USGovernmentMember_019ff2d2-7625-73fd-b508-01ece56e3001" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ff2d2-7625-7e01-8103-473f89d28f74" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019ff2d2-7625-702d-b893-dcfd47b1a9c6" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019ff2d2-7625-7e01-8103-473f89d28f74" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/RevenueNarrativeDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#RevenueNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/RevenueNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_019ff2d2-7625-7db5-9640-e9b2d04fbc32" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_019ff2d2-7625-78ba-aa68-3a6a7290548c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019ff2d2-7625-7db5-9640-e9b2d04fbc32" xlink:to="loc_us-gaap_ConcentrationRiskTable_019ff2d2-7625-78ba-aa68-3a6a7290548c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019ff2d2-7625-7782-ab50-7973a441158e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019ff2d2-7625-78ba-aa68-3a6a7290548c" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019ff2d2-7625-7782-ab50-7973a441158e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ff2d2-7625-7782-ab50-7973a441158e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019ff2d2-7625-7782-ab50-7973a441158e" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ff2d2-7625-7782-ab50-7973a441158e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ff2d2-7625-77f0-ba3a-378011933d0e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019ff2d2-7625-7782-ab50-7973a441158e" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ff2d2-7625-77f0-ba3a-378011933d0e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_019ff2d2-7625-7518-b245-efc9ed6325b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019ff2d2-7625-77f0-ba3a-378011933d0e" xlink:to="loc_us-gaap_AccountsReceivableMember_019ff2d2-7625-7518-b245-efc9ed6325b0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019ff2d2-7625-7a7e-aebe-734a1dc6b4e5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019ff2d2-7625-78ba-aa68-3a6a7290548c" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019ff2d2-7625-7a7e-aebe-734a1dc6b4e5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019ff2d2-7625-7a7e-aebe-734a1dc6b4e5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019ff2d2-7625-7a7e-aebe-734a1dc6b4e5" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019ff2d2-7625-7a7e-aebe-734a1dc6b4e5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019ff2d2-7625-7048-88a0-026ca1bc2b46" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019ff2d2-7625-7a7e-aebe-734a1dc6b4e5" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019ff2d2-7625-7048-88a0-026ca1bc2b46" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_PrimeContractsWithTheUSGovernmentMember_019ff2d2-7625-7076-acf4-2fdaca989564" xlink:href="irdm-20260930.xsd#irdm_PrimeContractsWithTheUSGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019ff2d2-7625-7048-88a0-026ca1bc2b46" xlink:to="loc_irdm_PrimeContractsWithTheUSGovernmentMember_019ff2d2-7625-7076-acf4-2fdaca989564" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019ff2d2-7625-7627-8f86-3c808126b55c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019ff2d2-7625-7048-88a0-026ca1bc2b46" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019ff2d2-7625-7627-8f86-3c808126b55c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019ff2d2-7625-7477-8cbb-e7abc3b6e5f5" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019ff2d2-7625-78ba-aa68-3a6a7290548c" xlink:to="loc_srt_ProductOrServiceAxis_019ff2d2-7625-7477-8cbb-e7abc3b6e5f5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7477-8cbb-e7abc3b6e5f5_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019ff2d2-7625-7477-8cbb-e7abc3b6e5f5" xlink:to="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-7477-8cbb-e7abc3b6e5f5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-78ac-9166-f9f5f38cce43" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019ff2d2-7625-7477-8cbb-e7abc3b6e5f5" xlink:to="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-78ac-9166-f9f5f38cce43" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_PrimeContractsWithTheUSGovernmentMember_019ff2d2-7625-7d6d-a4be-52cd45aef88a" xlink:href="irdm-20260930.xsd#irdm_PrimeContractsWithTheUSGovernmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019ff2d2-7625-78ac-9166-f9f5f38cce43" xlink:to="loc_irdm_PrimeContractsWithTheUSGovernmentMember_019ff2d2-7625-7d6d-a4be-52cd45aef88a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019ff2d2-7625-7351-b562-e7f6d0a02b9a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019ff2d2-7625-7db5-9640-e9b2d04fbc32" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019ff2d2-7625-7351-b562-e7f6d0a02b9a" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/RevenueSummaryofContractCostsDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#RevenueSummaryofContractCostsDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/RevenueSummaryofContractCostsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostLineItems_019ff2d2-7625-7012-9b31-c4df4742513f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CapitalizedContractCostLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostTable_019ff2d2-7625-79dd-a6ce-9710375ddb8f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CapitalizedContractCostTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_019ff2d2-7625-7012-9b31-c4df4742513f" xlink:to="loc_us-gaap_CapitalizedContractCostTable_019ff2d2-7625-79dd-a6ce-9710375ddb8f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostAxis_019ff2d2-7625-7890-8a18-27e18d768e27" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CapitalizedContractCostAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_CapitalizedContractCostTable_019ff2d2-7625-79dd-a6ce-9710375ddb8f" xlink:to="loc_us-gaap_CapitalizedContractCostAxis_019ff2d2-7625-7890-8a18-27e18d768e27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_019ff2d2-7625-7890-8a18-27e18d768e27_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_019ff2d2-7625-7890-8a18-27e18d768e27" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_019ff2d2-7625-7890-8a18-27e18d768e27_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CapitalizedContractCostDomain_019ff2d2-7625-7958-9a7b-8a1094e953ae" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CapitalizedContractCostDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CapitalizedContractCostAxis_019ff2d2-7625-7890-8a18-27e18d768e27" xlink:to="loc_us-gaap_CapitalizedContractCostDomain_019ff2d2-7625-7958-9a7b-8a1094e953ae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_CommissionsMember_019ff2d2-7625-7379-aacf-ed5ff1b5c060" xlink:href="irdm-20260930.xsd#irdm_CommissionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostDomain_019ff2d2-7625-7958-9a7b-8a1094e953ae" xlink:to="loc_irdm_CommissionsMember_019ff2d2-7625-7379-aacf-ed5ff1b5c060" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_OtherContractAssetsMember_019ff2d2-7625-7fda-8250-b74f6c02938e" xlink:href="irdm-20260930.xsd#irdm_OtherContractAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostDomain_019ff2d2-7625-7958-9a7b-8a1094e953ae" xlink:to="loc_irdm_OtherContractAssetsMember_019ff2d2-7625-7fda-8250-b74f6c02938e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerAssetNet_019ff2d2-7625-7e7d-80a1-42eed3671ada" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ContractWithCustomerAssetNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CapitalizedContractCostLineItems_019ff2d2-7625-7012-9b31-c4df4742513f" xlink:to="loc_us-gaap_ContractWithCustomerAssetNet_019ff2d2-7625-7e7d-80a1-42eed3671ada" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/LeasesDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#LeasesDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/LeasesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorLeaseDescriptionLineItems_019ff2d2-7625-75c1-b234-5ea67734fd4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorLeaseDescriptionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorLeaseDescriptionTable_019ff2d2-7625-7fcd-9e77-413ab2e5ee42" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorLeaseDescriptionTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019ff2d2-7625-75c1-b234-5ea67734fd4c" xlink:to="loc_us-gaap_LessorLeaseDescriptionTable_019ff2d2-7625-7fcd-9e77-413ab2e5ee42" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ff2d2-7625-7235-bf5a-9ee85081aac7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LessorLeaseDescriptionTable_019ff2d2-7625-7fcd-9e77-413ab2e5ee42" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ff2d2-7625-7235-bf5a-9ee85081aac7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ff2d2-7625-7235-bf5a-9ee85081aac7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ff2d2-7625-7235-bf5a-9ee85081aac7" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ff2d2-7625-7235-bf5a-9ee85081aac7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ff2d2-7625-7bcf-b085-41bda748b7a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019ff2d2-7625-7235-bf5a-9ee85081aac7" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ff2d2-7625-7bcf-b085-41bda748b7a5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_NextGenerationSatellitesMember_019ff2d2-7625-76dd-878e-1ec3ee0983fd" xlink:href="irdm-20260930.xsd#irdm_NextGenerationSatellitesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019ff2d2-7625-7bcf-b085-41bda748b7a5" xlink:to="loc_irdm_NextGenerationSatellitesMember_019ff2d2-7625-76dd-878e-1ec3ee0983fd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019ff2d2-7625-7b0e-9c81-cef7f8ce1f62" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PropertyPlantAndEquipmentUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019ff2d2-7625-75c1-b234-5ea67734fd4c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentUsefulLife_019ff2d2-7625-7b0e-9c81-cef7f8ce1f62" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingLeaseLeaseIncome_019ff2d2-7625-7a3c-aaa9-f0a38d1227e4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OperatingLeaseLeaseIncome"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019ff2d2-7625-75c1-b234-5ea67734fd4c" xlink:to="loc_us-gaap_OperatingLeaseLeaseIncome_019ff2d2-7625-7a3c-aaa9-f0a38d1227e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedRemainderOfFiscalYear_019ff2d2-7625-787e-b327-2d315490a10f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019ff2d2-7625-75c1-b234-5ea67734fd4c" xlink:to="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedRemainderOfFiscalYear_019ff2d2-7625-787e-b327-2d315490a10f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextTwelveMonths_019ff2d2-7625-7d53-8e27-87c47909d1d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019ff2d2-7625-75c1-b234-5ea67734fd4c" xlink:to="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedNextTwelveMonths_019ff2d2-7625-7d53-8e27-87c47909d1d5" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears_019ff2d2-7625-7ae8-9834-81b135f4d77b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019ff2d2-7625-75c1-b234-5ea67734fd4c" xlink:to="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedTwoYears_019ff2d2-7625-7ae8-9834-81b135f4d77b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThreeYears_019ff2d2-7625-7b01-88a5-75ec4af77248" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedThreeYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019ff2d2-7625-75c1-b234-5ea67734fd4c" xlink:to="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThreeYears_019ff2d2-7625-7b01-88a5-75ec4af77248" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFourYears_019ff2d2-7625-7939-a830-1a26cab70daa" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedFourYears"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019ff2d2-7625-75c1-b234-5ea67734fd4c" xlink:to="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedFourYears_019ff2d2-7625-7939-a830-1a26cab70daa" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter_019ff2d2-7625-7337-95ed-7b4225ff8b53" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019ff2d2-7625-75c1-b234-5ea67734fd4c" xlink:to="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceivedThereafter_019ff2d2-7625-7337-95ed-7b4225ff8b53" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceived_019ff2d2-7625-70bf-84b2-9e9178da8e5b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_LessorOperatingLeasePaymentsToBeReceived"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LessorLeaseDescriptionLineItems_019ff2d2-7625-75c1-b234-5ea67734fd4c" xlink:to="loc_us-gaap_LessorOperatingLeasePaymentsToBeReceived_019ff2d2-7625-70bf-84b2-9e9178da8e5b" xlink:type="arc" order="8"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/StockBasedCompensationNarrativeDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#StockBasedCompensationNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/StockBasedCompensationNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-7d62-ac16-fffb498dfcbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ff2d2-7625-7073-ab24-d4907ea96ed2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-7d62-ac16-fffb498dfcbf" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ff2d2-7625-7073-ab24-d4907ea96ed2" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7c4d-8430-05c71327c0b0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ff2d2-7625-7073-ab24-d4907ea96ed2" xlink:to="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7c4d-8430-05c71327c0b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7c4d-8430-05c71327c0b0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7c4d-8430-05c71327c0b0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7c4d-8430-05c71327c0b0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7a1d-8b79-16734d59893f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7c4d-8430-05c71327c0b0" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7a1d-8b79-16734d59893f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019ff2d2-7625-7302-ae79-6fa50561ec25" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7a1d-8b79-16734d59893f" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019ff2d2-7625-7302-ae79-6fa50561ec25" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_ServiceBasedRSUMember_019ff2d2-7625-716e-9400-550b9bba8753" xlink:href="irdm-20260930.xsd#irdm_ServiceBasedRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7a1d-8b79-16734d59893f" xlink:to="loc_irdm_ServiceBasedRSUMember_019ff2d2-7625-716e-9400-550b9bba8753" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019ff2d2-7625-7f73-ba7a-cd5c39b8a612" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7a1d-8b79-16734d59893f" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019ff2d2-7625-7f73-ba7a-cd5c39b8a612" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019ff2d2-7625-7e4e-b77c-2de01a0e5fd8" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7a1d-8b79-16734d59893f" xlink:to="loc_us-gaap_PerformanceSharesMember_019ff2d2-7625-7e4e-b77c-2de01a0e5fd8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_OutstandingRestrictedStockUnitsMember_019ff2d2-7625-79e8-b70e-19a18e708822" xlink:href="irdm-20260930.xsd#irdm_OutstandingRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7a1d-8b79-16734d59893f" xlink:to="loc_irdm_OutstandingRestrictedStockUnitsMember_019ff2d2-7625-79e8-b70e-19a18e708822" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019ff2d2-7625-7626-a04e-d6633f625083" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ff2d2-7625-7073-ab24-d4907ea96ed2" xlink:to="loc_srt_TitleOfIndividualAxis_019ff2d2-7625-7626-a04e-d6633f625083" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ff2d2-7625-7626-a04e-d6633f625083_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_019ff2d2-7625-7626-a04e-d6633f625083" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ff2d2-7625-7626-a04e-d6633f625083_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ff2d2-7625-79c4-ad6b-31b33ce8ac14" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_019ff2d2-7625-7626-a04e-d6633f625083" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ff2d2-7625-79c4-ad6b-31b33ce8ac14" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_DirectorMember_019ff2d2-7625-7a40-8611-c142159e2997" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_DirectorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ff2d2-7625-79c4-ad6b-31b33ce8ac14" xlink:to="loc_srt_DirectorMember_019ff2d2-7625-7a40-8611-c142159e2997" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ExecutiveOfficerMember_019ff2d2-7625-7ee4-89c0-47a9e566b7cd" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ExecutiveOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ff2d2-7625-79c4-ad6b-31b33ce8ac14" xlink:to="loc_srt_ExecutiveOfficerMember_019ff2d2-7625-7ee4-89c0-47a9e566b7cd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusAxis_019ff2d2-7625-7817-8e56-7d668c097d64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ff2d2-7625-7073-ab24-d4907ea96ed2" xlink:to="loc_us-gaap_GranteeStatusAxis_019ff2d2-7625-7817-8e56-7d668c097d64" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_019ff2d2-7625-7817-8e56-7d668c097d64_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_GranteeStatusAxis_019ff2d2-7625-7817-8e56-7d668c097d64" xlink:to="loc_us-gaap_GranteeStatusDomain_019ff2d2-7625-7817-8e56-7d668c097d64_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GranteeStatusDomain_019ff2d2-7625-7b27-89cc-f54a46265b50" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_GranteeStatusDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_GranteeStatusAxis_019ff2d2-7625-7817-8e56-7d668c097d64" xlink:to="loc_us-gaap_GranteeStatusDomain_019ff2d2-7625-7b27-89cc-f54a46265b50" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_019ff2d2-7625-7f79-aa8e-1a43ead09842" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedPaymentArrangementNonemployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_019ff2d2-7625-7b27-89cc-f54a46265b50" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementNonemployeeMember_019ff2d2-7625-7f79-aa8e-1a43ead09842" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_019ff2d2-7625-75fb-917e-085f27da9303" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedPaymentArrangementEmployeeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_GranteeStatusDomain_019ff2d2-7625-7b27-89cc-f54a46265b50" xlink:to="loc_us-gaap_ShareBasedPaymentArrangementEmployeeMember_019ff2d2-7625-75fb-917e-085f27da9303" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_019ff2d2-7625-775b-89c2-9a3fa32c2b6c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ff2d2-7625-7073-ab24-d4907ea96ed2" xlink:to="loc_us-gaap_VestingAxis_019ff2d2-7625-775b-89c2-9a3fa32c2b6c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019ff2d2-7625-775b-89c2-9a3fa32c2b6c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_019ff2d2-7625-775b-89c2-9a3fa32c2b6c" xlink:to="loc_us-gaap_VestingDomain_019ff2d2-7625-775b-89c2-9a3fa32c2b6c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019ff2d2-7625-762e-a6a9-1632788f1a83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_019ff2d2-7625-775b-89c2-9a3fa32c2b6c" xlink:to="loc_us-gaap_VestingDomain_019ff2d2-7625-762e-a6a9-1632788f1a83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019ff2d2-7625-7e11-a103-6dbd8ba56753" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019ff2d2-7625-762e-a6a9-1632788f1a83" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019ff2d2-7625-7e11-a103-6dbd8ba56753" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019ff2d2-7625-7a22-baf7-9b1ac29b2773" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019ff2d2-7625-762e-a6a9-1632788f1a83" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheTwoMember_019ff2d2-7625-7a22-baf7-9b1ac29b2773" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ff2d2-7625-758b-96ef-ba621143544d" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ff2d2-7625-7073-ab24-d4907ea96ed2" xlink:to="loc_srt_RangeAxis_019ff2d2-7625-758b-96ef-ba621143544d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ff2d2-7625-758b-96ef-ba621143544d_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ff2d2-7625-758b-96ef-ba621143544d" xlink:to="loc_srt_RangeMember_019ff2d2-7625-758b-96ef-ba621143544d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ff2d2-7625-752f-b5cf-2b92877dd6d0" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ff2d2-7625-758b-96ef-ba621143544d" xlink:to="loc_srt_RangeMember_019ff2d2-7625-752f-b5cf-2b92877dd6d0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019ff2d2-7625-7cf9-bb50-2be81165987a" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ff2d2-7625-752f-b5cf-2b92877dd6d0" xlink:to="loc_srt_MinimumMember_019ff2d2-7625-7cf9-bb50-2be81165987a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019ff2d2-7625-7dc8-8421-16233f4ade40" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ff2d2-7625-752f-b5cf-2b92877dd6d0" xlink:to="loc_srt_MaximumMember_019ff2d2-7625-7dc8-8421-16233f4ade40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019ff2d2-7625-700b-9f94-0d8a137cfebe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-7d62-ac16-fffb498dfcbf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019ff2d2-7625-700b-9f94-0d8a137cfebe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_ShareBaseCompensationAwardReductionInSharesAvailableForIssuanceBySharesIssuedPursuantToAnyAppreciationAward_019ff2d2-7625-7044-a492-4d5c0c021c4e" xlink:href="irdm-20260930.xsd#irdm_ShareBaseCompensationAwardReductionInSharesAvailableForIssuanceBySharesIssuedPursuantToAnyAppreciationAward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-7d62-ac16-fffb498dfcbf" xlink:to="loc_irdm_ShareBaseCompensationAwardReductionInSharesAvailableForIssuanceBySharesIssuedPursuantToAnyAppreciationAward_019ff2d2-7625-7044-a492-4d5c0c021c4e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_019ff2d2-7625-7cf2-846c-a74ef51030a5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-7d62-ac16-fffb498dfcbf" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_019ff2d2-7625-7cf2-846c-a74ef51030a5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_ShareBaseCompensationAwardReductionInSharesAvailableForIssuanceBySharesIssuedPursuantToAnyStockAwardThatIsNotAnAppreciationAward_019ff2d2-7625-744e-9928-f215b4058e2d" xlink:href="irdm-20260930.xsd#irdm_ShareBaseCompensationAwardReductionInSharesAvailableForIssuanceBySharesIssuedPursuantToAnyStockAwardThatIsNotAnAppreciationAward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-7d62-ac16-fffb498dfcbf" xlink:to="loc_irdm_ShareBaseCompensationAwardReductionInSharesAvailableForIssuanceBySharesIssuedPursuantToAnyStockAwardThatIsNotAnAppreciationAward_019ff2d2-7625-744e-9928-f215b4058e2d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019ff2d2-7625-731d-8ee8-5667608c748d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-7d62-ac16-fffb498dfcbf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingPeriod1_019ff2d2-7625-731d-8ee8-5667608c748d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_019ff2d2-7625-7283-b64a-08a89a5e4d81" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-7d62-ac16-fffb498dfcbf" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardAwardVestingRightsPercentage_019ff2d2-7625-7283-b64a-08a89a5e4d81" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ff2d2-7625-7472-90b0-28b0d4aea545" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-7d62-ac16-fffb498dfcbf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ff2d2-7625-7472-90b0-28b0d4aea545" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockGrantedDuringPeriodValueSharebasedCompensationGross_019ff2d2-7625-7335-b285-87b97596c736" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_StockGrantedDuringPeriodValueSharebasedCompensationGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-7d62-ac16-fffb498dfcbf" xlink:to="loc_us-gaap_StockGrantedDuringPeriodValueSharebasedCompensationGross_019ff2d2-7625-7335-b285-87b97596c736" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherShareIncreaseDecrease_019ff2d2-7625-787c-b89e-9102cf8f44fe" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherShareIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-7d62-ac16-fffb498dfcbf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOtherShareIncreaseDecrease_019ff2d2-7625-787c-b89e-9102cf8f44fe" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_SharebasedCompensationArrangementbySharebasedPaymentAwardAwardPerformancePeriod_019ff2d2-7625-73aa-b830-a8e398c890b8" xlink:href="irdm-20260930.xsd#irdm_SharebasedCompensationArrangementbySharebasedPaymentAwardAwardPerformancePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-7d62-ac16-fffb498dfcbf" xlink:to="loc_irdm_SharebasedCompensationArrangementbySharebasedPaymentAwardAwardPerformancePeriod_019ff2d2-7625-73aa-b830-a8e398c890b8" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardRatablyVestAfter_019ff2d2-7625-7330-b24c-4c81566e79ff" xlink:href="irdm-20260930.xsd#irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardRatablyVestAfter"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-7d62-ac16-fffb498dfcbf" xlink:to="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardRatablyVestAfter_019ff2d2-7625-7330-b24c-4c81566e79ff" xlink:type="arc" order="10"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/StockBasedCompensationOutstandingRSUsDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#StockBasedCompensationOutstandingRSUsDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/StockBasedCompensationOutstandingRSUsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-75a4-9763-a84b6b1272bf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ff2d2-7625-7bd5-bb7e-47fd3525f9d5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-75a4-9763-a84b6b1272bf" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ff2d2-7625-7bd5-bb7e-47fd3525f9d5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7462-bee0-2eb9b9f2aa10" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019ff2d2-7625-7bd5-bb7e-47fd3525f9d5" xlink:to="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7462-bee0-2eb9b9f2aa10" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7462-bee0-2eb9b9f2aa10_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7462-bee0-2eb9b9f2aa10" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7462-bee0-2eb9b9f2aa10_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-734e-9867-de2b66480d56" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7462-bee0-2eb9b9f2aa10" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-734e-9867-de2b66480d56" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_OutstandingRestrictedStockUnitsMember_019ff2d2-7625-7572-a9d4-fe449a62d2fe" xlink:href="irdm-20260930.xsd#irdm_OutstandingRestrictedStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-734e-9867-de2b66480d56" xlink:to="loc_irdm_OutstandingRestrictedStockUnitsMember_019ff2d2-7625-7572-a9d4-fe449a62d2fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ff2d2-7625-703c-a7b7-337dd913ac5e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-75a4-9763-a84b6b1272bf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ff2d2-7625-703c-a7b7-337dd913ac5e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingNumber_019ff2d2-7625-715b-95e2-7465a5927f26" xlink:href="irdm-20260930.xsd#irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ff2d2-7625-703c-a7b7-337dd913ac5e" xlink:to="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingNumber_019ff2d2-7625-715b-95e2-7465a5927f26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ff2d2-7625-79bf-83c1-bad5d94a37c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ff2d2-7625-703c-a7b7-337dd913ac5e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019ff2d2-7625-79bf-83c1-bad5d94a37c9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019ff2d2-7625-7c90-9701-306e1ec07f47" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ff2d2-7625-703c-a7b7-337dd913ac5e" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019ff2d2-7625-7c90-9701-306e1ec07f47" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriod_019ff2d2-7625-7788-bc72-d0ee8332595f" xlink:href="irdm-20260930.xsd#irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ff2d2-7625-703c-a7b7-337dd913ac5e" xlink:to="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriod_019ff2d2-7625-7788-bc72-d0ee8332595f" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingNumber_019ff2d2-7625-7f1f-bdd9-8b28c47f3c23" xlink:href="irdm-20260930.xsd#irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVested_019ff2d2-7625-76f8-a73b-a69eb1122e70" xlink:href="irdm-20260930.xsd#irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVested"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019ff2d2-7625-703c-a7b7-337dd913ac5e" xlink:to="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVested_019ff2d2-7625-76f8-a73b-a69eb1122e70" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ff2d2-7625-7f04-b848-222a9d060d40" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019ff2d2-7625-75a4-9763-a84b6b1272bf" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ff2d2-7625-7f04-b848-222a9d060d40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageGrantDateFairValue_019ff2d2-7625-7128-ad71-4277c9a090ac" xlink:href="irdm-20260930.xsd#irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ff2d2-7625-7f04-b848-222a9d060d40" xlink:to="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageGrantDateFairValue_019ff2d2-7625-7128-ad71-4277c9a090ac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedWeightedAverageGrantDateFairValue_019ff2d2-7625-7b26-a3c6-2db74d739092" xlink:href="irdm-20260930.xsd#irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ff2d2-7625-7f04-b848-222a9d060d40" xlink:to="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantedWeightedAverageGrantDateFairValue_019ff2d2-7625-7b26-a3c6-2db74d739092" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019ff2d2-7625-7297-a82f-c17e8aa60d23" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ff2d2-7625-7f04-b848-222a9d060d40" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019ff2d2-7625-7297-a82f-c17e8aa60d23" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriodWeightedAverageGrantDateFairValue_019ff2d2-7625-78c9-a9e2-195bf50a16aa" xlink:href="irdm-20260930.xsd#irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019ff2d2-7625-7f04-b848-222a9d060d40" xlink:to="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsReleasedInPeriodWeightedAverageGrantDateFairValue_019ff2d2-7625-78c9-a9e2-195bf50a16aa" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageGrantDateFairValue_019ff2d2-7625-7141-8538-9c306034aa9a" xlink:href="irdm-20260930.xsd#irdm_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsOutstandingWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/RelatedPartyTransactionsRelatedPartyTransactionsDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#RelatedPartyTransactionsRelatedPartyTransactionsDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/RelatedPartyTransactionsRelatedPartyTransactionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionLineItems_019ff2d2-7625-7134-b68c-d6884b20ada4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ff2d2-7625-7f7a-bf47-2ddcb84185c3" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ff2d2-7625-7134-b68c-d6884b20ada4" xlink:to="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ff2d2-7625-7f7a-bf47-2ddcb84185c3" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019ff2d2-7625-7081-a9d0-889bc9b15f0b" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ff2d2-7625-7f7a-bf47-2ddcb84185c3" xlink:to="loc_srt_RangeAxis_019ff2d2-7625-7081-a9d0-889bc9b15f0b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ff2d2-7625-7081-a9d0-889bc9b15f0b_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019ff2d2-7625-7081-a9d0-889bc9b15f0b" xlink:to="loc_srt_RangeMember_019ff2d2-7625-7081-a9d0-889bc9b15f0b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019ff2d2-7625-7506-9eb3-99f735390df6" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019ff2d2-7625-7081-a9d0-889bc9b15f0b" xlink:to="loc_srt_RangeMember_019ff2d2-7625-7506-9eb3-99f735390df6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019ff2d2-7625-7a4e-9799-07d8b793d388" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ff2d2-7625-7506-9eb3-99f735390df6" xlink:to="loc_srt_MaximumMember_019ff2d2-7625-7a4e-9799-07d8b793d388" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019ff2d2-7625-788f-9494-1a740f038b05" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019ff2d2-7625-7506-9eb3-99f735390df6" xlink:to="loc_srt_MinimumMember_019ff2d2-7625-788f-9494-1a740f038b05" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionAxis_019ff2d2-7625-7a21-a2fd-55f7012b2d1c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ff2d2-7625-7f7a-bf47-2ddcb84185c3" xlink:to="loc_us-gaap_RelatedPartyTransactionAxis_019ff2d2-7625-7a21-a2fd-55f7012b2d1c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ff2d2-7625-7a21-a2fd-55f7012b2d1c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ff2d2-7625-7a21-a2fd-55f7012b2d1c" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ff2d2-7625-7a21-a2fd-55f7012b2d1c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionDomain_019ff2d2-7625-74af-9dbd-8193214e9ee7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionAxis_019ff2d2-7625-7a21-a2fd-55f7012b2d1c" xlink:to="loc_us-gaap_RelatedPartyTransactionDomain_019ff2d2-7625-74af-9dbd-8193214e9ee7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_Aireon2022PreferredEquityInvestmentMember_019ff2d2-7625-772f-98e8-13795ffa5dee" xlink:href="irdm-20260930.xsd#irdm_Aireon2022PreferredEquityInvestmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ff2d2-7625-74af-9dbd-8193214e9ee7" xlink:to="loc_irdm_Aireon2022PreferredEquityInvestmentMember_019ff2d2-7625-772f-98e8-13795ffa5dee" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_HostingAgreementMember_019ff2d2-7625-7e33-ba36-2d01d0025f26" xlink:href="irdm-20260930.xsd#irdm_HostingAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ff2d2-7625-74af-9dbd-8193214e9ee7" xlink:to="loc_irdm_HostingAgreementMember_019ff2d2-7625-7e33-ba36-2d01d0025f26" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_PowerAgreementMember_019ff2d2-7625-7c24-90de-df30b3a60791" xlink:href="irdm-20260930.xsd#irdm_PowerAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ff2d2-7625-74af-9dbd-8193214e9ee7" xlink:to="loc_irdm_PowerAgreementMember_019ff2d2-7625-7c24-90de-df30b3a60791" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ServiceAgreementsMember_019ff2d2-7625-7e67-bbc0-4c6eee35386d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ServiceAgreementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ff2d2-7625-74af-9dbd-8193214e9ee7" xlink:to="loc_us-gaap_ServiceAgreementsMember_019ff2d2-7625-7e67-bbc0-4c6eee35386d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_AdministrativeAndSupportAgreementAccountsReceivableMember_019ff2d2-7625-75a3-bae2-090d250852c2" xlink:href="irdm-20260930.xsd#irdm_AdministrativeAndSupportAgreementAccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ff2d2-7625-74af-9dbd-8193214e9ee7" xlink:to="loc_irdm_AdministrativeAndSupportAgreementAccountsReceivableMember_019ff2d2-7625-75a3-bae2-090d250852c2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_AireonInvestorBridgeLoanMember_019ff2d2-7625-7022-a1ac-56c566bdd5f0" xlink:href="irdm-20260930.xsd#irdm_AireonInvestorBridgeLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionDomain_019ff2d2-7625-74af-9dbd-8193214e9ee7" xlink:to="loc_irdm_AireonInvestorBridgeLoanMember_019ff2d2-7625-7022-a1ac-56c566bdd5f0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ff2d2-7625-7498-84f6-5b2cd6b1ef4f" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ff2d2-7625-7f7a-bf47-2ddcb84185c3" xlink:to="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ff2d2-7625-7498-84f6-5b2cd6b1ef4f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019ff2d2-7625-7498-84f6-5b2cd6b1ef4f_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ff2d2-7625-7498-84f6-5b2cd6b1ef4f" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019ff2d2-7625-7498-84f6-5b2cd6b1ef4f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_EquityMethodInvesteeNameDomain_019ff2d2-7625-752a-a40f-bab166536448" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_EquityMethodInvesteeNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis_019ff2d2-7625-7498-84f6-5b2cd6b1ef4f" xlink:to="loc_srt_EquityMethodInvesteeNameDomain_019ff2d2-7625-752a-a40f-bab166536448" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherInvesteesMember_019ff2d2-7625-7a11-a96f-1b95061a167b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_OtherInvesteesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019ff2d2-7625-752a-a40f-bab166536448" xlink:to="loc_us-gaap_OtherInvesteesMember_019ff2d2-7625-7a11-a96f-1b95061a167b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_AireonMember_019ff2d2-7625-7989-9efd-d2c4de17b9d5" xlink:href="irdm-20260930.xsd#irdm_AireonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_EquityMethodInvesteeNameDomain_019ff2d2-7625-752a-a40f-bab166536448" xlink:to="loc_irdm_AireonMember_019ff2d2-7625-7989-9efd-d2c4de17b9d5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ff2d2-7625-7d17-a903-9240c5aada6d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyTransactionsByRelatedPartyAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ff2d2-7625-7f7a-bf47-2ddcb84185c3" xlink:to="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ff2d2-7625-7d17-a903-9240c5aada6d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ff2d2-7625-7d17-a903-9240c5aada6d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ff2d2-7625-7d17-a903-9240c5aada6d" xlink:to="loc_us-gaap_RelatedPartyDomain_019ff2d2-7625-7d17-a903-9240c5aada6d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RelatedPartyDomain_019ff2d2-7625-7c8b-9a64-2bdc73ddbd3a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RelatedPartyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RelatedPartyTransactionsByRelatedPartyAxis_019ff2d2-7625-7d17-a903-9240c5aada6d" xlink:to="loc_us-gaap_RelatedPartyDomain_019ff2d2-7625-7c8b-9a64-2bdc73ddbd3a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvesteeMember_019ff2d2-7625-7976-9101-aed4249de6d7" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvesteeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019ff2d2-7625-7c8b-9a64-2bdc73ddbd3a" xlink:to="loc_us-gaap_EquityMethodInvesteeMember_019ff2d2-7625-7976-9101-aed4249de6d7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_019ff2d2-7625-78be-897d-0490bad8bd3c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyDomain_019ff2d2-7625-7c8b-9a64-2bdc73ddbd3a" xlink:to="loc_us-gaap_EquityMethodInvestmentNonconsolidatedInvesteeDomain_019ff2d2-7625-78be-897d-0490bad8bd3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualAxis_019ff2d2-7625-7bca-80d1-3644fa8d5fbf" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ff2d2-7625-7f7a-bf47-2ddcb84185c3" xlink:to="loc_srt_TitleOfIndividualAxis_019ff2d2-7625-7bca-80d1-3644fa8d5fbf" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ff2d2-7625-7bca-80d1-3644fa8d5fbf_default" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_TitleOfIndividualAxis_019ff2d2-7625-7bca-80d1-3644fa8d5fbf" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ff2d2-7625-7bca-80d1-3644fa8d5fbf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ff2d2-7625-7eda-959b-d85b565bad27" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_TitleOfIndividualWithRelationshipToEntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_TitleOfIndividualAxis_019ff2d2-7625-7bca-80d1-3644fa8d5fbf" xlink:to="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ff2d2-7625-7eda-959b-d85b565bad27" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ExecutiveOfficerMember_019ff2d2-7625-745c-a44e-2429aa46c7fe" xlink:href="https://xbrl.fasb.org/srt/2026/elts/srt-2026.xsd#srt_ExecutiveOfficerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_TitleOfIndividualWithRelationshipToEntityDomain_019ff2d2-7625-7eda-959b-d85b565bad27" xlink:to="loc_srt_ExecutiveOfficerMember_019ff2d2-7625-745c-a44e-2429aa46c7fe" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7a43-ab51-cec654c6d272" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ff2d2-7625-7f7a-bf47-2ddcb84185c3" xlink:to="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7a43-ab51-cec654c6d272" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7a43-ab51-cec654c6d272_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7a43-ab51-cec654c6d272" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7a43-ab51-cec654c6d272_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7a41-901f-d0462326cd83" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7a43-ab51-cec654c6d272" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7a41-901f-d0462326cd83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019ff2d2-7625-7254-bf66-54ae720762e0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7a41-901f-d0462326cd83" xlink:to="loc_us-gaap_PerformanceSharesMember_019ff2d2-7625-7254-bf66-54ae720762e0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingAxis_019ff2d2-7625-7230-8b0b-d73cb4661da0" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfRelatedPartyTransactionsByRelatedPartyTable_019ff2d2-7625-7f7a-bf47-2ddcb84185c3" xlink:to="loc_us-gaap_VestingAxis_019ff2d2-7625-7230-8b0b-d73cb4661da0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019ff2d2-7625-7230-8b0b-d73cb4661da0_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VestingAxis_019ff2d2-7625-7230-8b0b-d73cb4661da0" xlink:to="loc_us-gaap_VestingDomain_019ff2d2-7625-7230-8b0b-d73cb4661da0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VestingDomain_019ff2d2-7625-7dc1-8ba3-8364ec24aac5" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_VestingDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VestingAxis_019ff2d2-7625-7230-8b0b-d73cb4661da0" xlink:to="loc_us-gaap_VestingDomain_019ff2d2-7625-7dc1-8ba3-8364ec24aac5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019ff2d2-7625-7b13-987f-0fef693b8768" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationAwardTrancheOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VestingDomain_019ff2d2-7625-7dc1-8ba3-8364ec24aac5" xlink:to="loc_us-gaap_ShareBasedCompensationAwardTrancheOneMember_019ff2d2-7625-7b13-987f-0fef693b8768" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsForProceedsFromInvestments_019ff2d2-7625-7994-87e3-86fa0e499929" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_PaymentsForProceedsFromInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ff2d2-7625-7134-b68c-d6884b20ada4" xlink:to="loc_us-gaap_PaymentsForProceedsFromInvestments_019ff2d2-7625-7994-87e3-86fa0e499929" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019ff2d2-7625-719a-9690-b40361d5fbdc" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestmentOwnershipPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ff2d2-7625-7134-b68c-d6884b20ada4" xlink:to="loc_us-gaap_EquityMethodInvestmentOwnershipPercentage_019ff2d2-7625-719a-9690-b40361d5fbdc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityMethodInvestments_019ff2d2-7625-730a-8af8-205c2c49c581" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EquityMethodInvestments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ff2d2-7625-7134-b68c-d6884b20ada4" xlink:to="loc_us-gaap_EquityMethodInvestments_019ff2d2-7625-730a-8af8-205c2c49c581" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Revenues_019ff2d2-7625-747e-9fae-68ebf91f231a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Revenues"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ff2d2-7625-7134-b68c-d6884b20ada4" xlink:to="loc_us-gaap_Revenues_019ff2d2-7625-747e-9fae-68ebf91f231a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NontradeReceivables_019ff2d2-7625-74c8-acb2-5403d7738ff2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NontradeReceivables"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ff2d2-7625-7134-b68c-d6884b20ada4" xlink:to="loc_us-gaap_NontradeReceivables_019ff2d2-7625-74c8-acb2-5403d7738ff2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_InvestorBridgeLoanCommitment_019ff2d2-7625-7dd1-84b1-7427a743274d" xlink:href="irdm-20260930.xsd#irdm_InvestorBridgeLoanCommitment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ff2d2-7625-7134-b68c-d6884b20ada4" xlink:to="loc_irdm_InvestorBridgeLoanCommitment_019ff2d2-7625-7dd1-84b1-7427a743274d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BridgeLoan_019ff2d2-7625-7513-a90d-5f3d8811a985" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BridgeLoan"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RelatedPartyTransactionLineItems_019ff2d2-7625-7134-b68c-d6884b20ada4" xlink:to="loc_us-gaap_BridgeLoan_019ff2d2-7625-7513-a90d-5f3d8811a985" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/NetIncomeLossPerShareScheduleofEarningsPerShareBasicandDilutedDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#NetIncomeLossPerShareScheduleofEarningsPerShareBasicandDilutedDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/NetIncomeLossPerShareScheduleofEarningsPerShareBasicandDilutedDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasicLineItems_019ff2d2-7625-7880-b235-81683ef0bbd2" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasicLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_019ff2d2-7625-7efb-a0f6-f0e1c6b5ff71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_019ff2d2-7625-7880-b235-81683ef0bbd2" xlink:to="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_019ff2d2-7625-7efb-a0f6-f0e1c6b5ff71" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7ef7-94b3-cf4456b30026" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEarningsPerShareBasicByCommonClassTable_019ff2d2-7625-7efb-a0f6-f0e1c6b5ff71" xlink:to="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7ef7-94b3-cf4456b30026" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7ef7-94b3-cf4456b30026_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7ef7-94b3-cf4456b30026" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7ef7-94b3-cf4456b30026_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7f18-98a6-0e6e81d3d593" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019ff2d2-7625-7ef7-94b3-cf4456b30026" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7f18-98a6-0e6e81d3d593" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019ff2d2-7625-7fcf-bf37-fca75c1deb0a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7f18-98a6-0e6e81d3d593" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019ff2d2-7625-7fcf-bf37-fca75c1deb0a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockMember_019ff2d2-7625-7c5f-be04-36499b091d71" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_RestrictedStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019ff2d2-7625-7f18-98a6-0e6e81d3d593" xlink:to="loc_us-gaap_RestrictedStockMember_019ff2d2-7625-7c5f-be04-36499b091d71" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_019ff2d2-7625-71b7-a82e-ba6c930c8f67" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_019ff2d2-7625-7880-b235-81683ef0bbd2" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic_019ff2d2-7625-71b7-a82e-ba6c930c8f67" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019ff2d2-7625-78dd-9507-3f9d17269e13" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_019ff2d2-7625-7880-b235-81683ef0bbd2" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019ff2d2-7625-78dd-9507-3f9d17269e13" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment_019ff2d2-7625-75c3-af7f-d8584bdbf8bd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_019ff2d2-7625-7880-b235-81683ef0bbd2" xlink:to="loc_us-gaap_WeightedAverageNumberDilutedSharesOutstandingAdjustment_019ff2d2-7625-75c3-af7f-d8584bdbf8bd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019ff2d2-7625-7997-a962-ef1e1037e2c9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_019ff2d2-7625-7880-b235-81683ef0bbd2" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019ff2d2-7625-7997-a962-ef1e1037e2c9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019ff2d2-7625-7011-b3b6-9e3bd5cfefbf" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_019ff2d2-7625-7880-b235-81683ef0bbd2" xlink:to="loc_us-gaap_EarningsPerShareBasic_019ff2d2-7625-7011-b3b6-9e3bd5cfefbf" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019ff2d2-7625-778d-a7e7-2ed231de9704" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareBasicLineItems_019ff2d2-7625-7880-b235-81683ef0bbd2" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019ff2d2-7625-778d-a7e7-2ed231de9704" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.iridium.com/role/BusinessCombinationsAssetAcquisitionsTransactionbetweenEntitiesunderCommonControlandJointVentureFormationDetails" xlink:type="simple" xlink:href="irdm-20260930.xsd#BusinessCombinationsAssetAcquisitionsTransactionbetweenEntitiesunderCommonControlandJointVentureFormationDetails"/>
  <link:definitionLink xlink:role="http://www.iridium.com/role/BusinessCombinationsAssetAcquisitionsTransactionbetweenEntitiesunderCommonControlandJointVentureFormationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableLineItems_01a14bea-75e2-7fa5-815c-1cb7b9e0752d" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionEquityInterestIssuedOrIssuableTable_01a14bea-75e2-7119-b08c-77f6cb9abd2b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionEquityInterestIssuedOrIssuableTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableLineItems_01a14bea-75e2-7fa5-815c-1cb7b9e0752d" xlink:to="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionEquityInterestIssuedOrIssuableTable_01a14bea-75e2-7119-b08c-77f6cb9abd2b" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_01a14bea-75e2-7ed6-8ffb-06b06ddbb811" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfBusinessAcquisitionsByAcquisitionEquityInterestIssuedOrIssuableTable_01a14bea-75e2-7119-b08c-77f6cb9abd2b" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_01a14bea-75e2-7ed6-8ffb-06b06ddbb811" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a14bea-75e2-7ed6-8ffb-06b06ddbb811_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a14bea-75e2-7ed6-8ffb-06b06ddbb811" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a14bea-75e2-7ed6-8ffb-06b06ddbb811_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a14bea-75e2-7cdf-a5c7-d80f996dc3f4" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_01a14bea-75e2-7ed6-8ffb-06b06ddbb811" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a14bea-75e2-7cdf-a5c7-d80f996dc3f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_AireonMember_01a14bea-a45e-74cf-bcf3-3c6de6280179" xlink:href="irdm-20260930.xsd#irdm_AireonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a14bea-75e2-7cdf-a5c7-d80f996dc3f4" xlink:to="loc_irdm_AireonMember_01a14bea-a45e-74cf-bcf3-3c6de6280179" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_01a14bea-75e2-7f80-ba85-adf579ded093" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableLineItems_01a14bea-75e2-7fa5-815c-1cb7b9e0752d" xlink:to="loc_us-gaap_Goodwill_01a14bea-75e2-7f80-ba85-adf579ded093" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1_01a14c20-ed85-7d2f-8fd7-0118457d4a4c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableLineItems_01a14bea-75e2-7fa5-815c-1cb7b9e0752d" xlink:to="loc_us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireeFairValue1_01a14c20-ed85-7d2f-8fd7-0118457d4a4c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_01a14c4d-9170-72bd-9a28-03ab3d703971" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableLineItems_01a14bea-75e2-7fa5-815c-1cb7b9e0752d" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_01a14c4d-9170-72bd-9a28-03ab3d703971" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationConsiderationTransferred1_01a14c4e-55ce-76c2-951c-d180bf703030" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationConsiderationTransferred1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableLineItems_01a14bea-75e2-7fa5-815c-1cb7b9e0752d" xlink:to="loc_us-gaap_BusinessCombinationConsiderationTransferred1_01a14c4e-55ce-76c2-951c-d180bf703030" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireePercentage_01a14c52-0552-773a-be72-b1b76a4ab64c" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionEquityInterestsIssuedOrIssuableLineItems_01a14bea-75e2-7fa5-815c-1cb7b9e0752d" xlink:to="loc_us-gaap_BusinessCombinationStepAcquisitionEquityInterestInAcquireePercentage_01a14c52-0552-773a-be72-b1b76a4ab64c" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_01a14bf2-ee88-741f-8116-54b2afc10864" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable_01a14bf2-ee88-7d19-b4b0-484a3f1d6fec" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_IndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_01a14bf2-ee88-741f-8116-54b2afc10864" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable_01a14bf2-ee88-7d19-b4b0-484a3f1d6fec" xlink:type="arc" order="2" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_01a14bf4-4139-7335-ab5d-5333684e7272" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable_01a14bf2-ee88-7d19-b4b0-484a3f1d6fec" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_01a14bf4-4139-7335-ab5d-5333684e7272" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a14bf4-4139-7335-ab5d-5333684e7272_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_01a14bf4-4139-7787-98a2-acf91f4a7ee9" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:loc xlink:type="locator" xlink:label="loc_irdm_AireonMember_01a14bf4-7317-7d7a-991b-ebeadbee80b7" xlink:href="irdm-20260930.xsd#irdm_AireonMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a14bf4-ef50-7d3c-97cb-6132a776fd9e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsAcquiredAsPartOfBusinessCombinationTable_01a14bf2-ee88-7d19-b4b0-484a3f1d6fec" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a14bf4-ef50-7d3c-97cb-6132a776fd9e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a14bf4-ef50-7d3c-97cb-6132a776fd9e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a14bf4-ef50-7d3c-97cb-6132a776fd9e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a14bf4-ef50-7d3c-97cb-6132a776fd9e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a14bf4-ef50-7a34-b460-984552d4a0b1" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_01a14bf4-ef50-7d3c-97cb-6132a776fd9e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a14bf4-ef50-7a34-b460-984552d4a0b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_01a14bf5-4364-79bb-95b3-d90481e7fbbd" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TechnologyBasedIntangibleAssetsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a14bf4-ef50-7a34-b460-984552d4a0b1" xlink:to="loc_us-gaap_TechnologyBasedIntangibleAssetsMember_01a14bf5-4364-79bb-95b3-d90481e7fbbd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_01a14bf5-efd1-70bd-93b7-136782b30671" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a14bf4-ef50-7a34-b460-984552d4a0b1" xlink:to="loc_us-gaap_CustomerRelationshipsMember_01a14bf5-efd1-70bd-93b7-136782b30671" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TradeNamesMember_01a14bf6-5869-75bb-b18c-70b3fab7fd1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_TradeNamesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_01a14bf4-ef50-7a34-b460-984552d4a0b1" xlink:to="loc_us-gaap_TradeNamesMember_01a14bf6-5869-75bb-b18c-70b3fab7fd1e" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_01a14bf2-ee88-73bd-a7d3-2f4d879f3013" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_FinitelivedIntangibleAssetsAcquired1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_01a14bf2-ee88-741f-8116-54b2afc10864" xlink:to="loc_us-gaap_FinitelivedIntangibleAssetsAcquired1_01a14bf2-ee88-73bd-a7d3-2f4d879f3013" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_01a14bf9-f571-75dc-a262-6976604a57eb" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredIndefiniteLivedIntangibleAssetsLineItems_01a14bf2-ee88-741f-8116-54b2afc10864" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_01a14bf9-f571-75dc-a262-6976604a57eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_01a14bff-e6ef-78c0-956c-a53a2afbf810" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_01a14bff-e6ef-7bc2-bbe5-6ffce0410e64" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_01a14bff-e6ef-78c0-956c-a53a2afbf810" xlink:to="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentsTable_01a14bff-e6ef-7bc2-bbe5-6ffce0410e64" xlink:type="arc" order="3" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_01a14bff-e6ef-7325-b8f0-52ef14063d1e" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_01a14bff-e6ef-78c0-956c-a53a2afbf810" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationEarningsOrLossOfAcquireeSinceAcquisitionDateActual_01a14bff-e6ef-7325-b8f0-52ef14063d1e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_01a14c00-ac86-75c4-ae85-5538d5fbe63b" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_01a14bff-e6ef-78c0-956c-a53a2afbf810" xlink:to="loc_us-gaap_BusinessCombinationProFormaInformationRevenueOfAcquireeSinceAcquisitionDateActual_01a14c00-ac86-75c4-ae85-5538d5fbe63b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_01a14c02-06b7-7810-88ea-cb3d2011c3f6" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_01a14bff-e6ef-78c0-956c-a53a2afbf810" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaRevenue_01a14c02-06b7-7810-88ea-cb3d2011c3f6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_01a14c03-41cb-7366-9c80-c3119d436d21" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionProFormaInformationNonrecurringAdjustmentLineItems_01a14bff-e6ef-78c0-956c-a53a2afbf810" xlink:to="loc_us-gaap_BusinessAcquisitionsProFormaNetIncomeLoss_01a14c03-41cb-7366-9c80-c3119d436d21" xlink:type="arc" order="3"/>
  </link:definitionLink>
</link:linkbase>
