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

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:01a05334-190b-7693-8db1-371efe7673da,g:dd8c5a91-6b0d-4a6f-8ec1-1f7a0ac5ecf1-->
<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.blacksky.com/role/Cover" xlink:type="simple" xlink:href="bksy-20260910.xsd#Cover"/>
  <link:definitionLink xlink:role="http://www.blacksky.com/role/Cover" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationLineItems_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_DocumentInformationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_DocumentInformationTable_01a05334-190b-7eb2-831f-7bf3babc13a7" 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_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_DocumentInformationTable_01a05334-190b-7eb2-831f-7bf3babc13a7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementClassOfStockAxis_01a05334-190b-7033-bede-d2e6346e6725" 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_01a05334-190b-7eb2-831f-7bf3babc13a7" xlink:to="loc_us-gaap_StatementClassOfStockAxis_01a05334-190b-7033-bede-d2e6346e6725" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a05334-190b-7033-bede-d2e6346e6725_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_01a05334-190b-7033-bede-d2e6346e6725" xlink:to="loc_us-gaap_ClassOfStockDomain_01a05334-190b-7033-bede-d2e6346e6725_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ClassOfStockDomain_01a05334-190b-787a-a544-2b0104da54dc" 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_01a05334-190b-7033-bede-d2e6346e6725" xlink:to="loc_us-gaap_ClassOfStockDomain_01a05334-190b-787a-a544-2b0104da54dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonClassAMember_01a05334-190b-7620-95cd-7ee32f23800a" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_CommonClassAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a05334-190b-787a-a544-2b0104da54dc" xlink:to="loc_us-gaap_CommonClassAMember_01a05334-190b-7620-95cd-7ee32f23800a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WarrantMember_01a05334-190b-78ee-a50a-25d997100f6f" xlink:href="https://xbrl.fasb.org/us-gaap/2026/elts/us-gaap-2026.xsd#us-gaap_WarrantMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ClassOfStockDomain_01a05334-190b-787a-a544-2b0104da54dc" xlink:to="loc_us-gaap_WarrantMember_01a05334-190b-78ee-a50a-25d997100f6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_Security12bTitle_01a05334-190b-7e03-9a07-e9802d2bd999" 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_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_Security12bTitle_01a05334-190b-7e03-9a07-e9802d2bd999" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_TradingSymbol_01a05334-190b-7ebf-a34f-f14a76ebb02b" 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_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_TradingSymbol_01a05334-190b-7ebf-a34f-f14a76ebb02b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SecurityExchangeName_01a05334-190b-7a56-a4d5-b3e00029f6cb" 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_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_SecurityExchangeName_01a05334-190b-7a56-a4d5-b3e00029f6cb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityCentralIndexKey_01a05334-190b-7016-a9cc-45426a66ea5e" 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_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_EntityCentralIndexKey_01a05334-190b-7016-a9cc-45426a66ea5e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_AmendmentFlag_01a05334-190b-7933-9e74-6df85cb63e5b" 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_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_AmendmentFlag_01a05334-190b-7933-9e74-6df85cb63e5b" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_WrittenCommunications_01a05334-190b-7b68-8a57-427179aca372" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_WrittenCommunications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_WrittenCommunications_01a05334-190b-7b68-8a57-427179aca372" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_SolicitingMaterial_01a05334-190b-7b4f-a7b1-fcd7d3dcb85c" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_SolicitingMaterial"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_SolicitingMaterial_01a05334-190b-7b4f-a7b1-fcd7d3dcb85c" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementTenderOffer_01a05334-190b-72bf-9259-657ebb263acf" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_PreCommencementTenderOffer_01a05334-190b-72bf-9259-657ebb263acf" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_PreCommencementIssuerTenderOffer_01a05334-190b-78df-adf9-01cfefd429fa" xlink:href="https://xbrl.sec.gov/dei/2026/dei-2026.xsd#dei_PreCommencementIssuerTenderOffer"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_DocumentInformationLineItems_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_PreCommencementIssuerTenderOffer_01a05334-190b-78df-adf9-01cfefd429fa" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityEmergingGrowthCompany_01a05334-190b-7073-ae6a-46ca65b8a8af" 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_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_EntityEmergingGrowthCompany_01a05334-190b-7073-ae6a-46ca65b8a8af" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityIncorporationStateCountryCode_01a05334-190b-789a-812c-180ae05db5de" 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_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_EntityIncorporationStateCountryCode_01a05334-190b-789a-812c-180ae05db5de" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityTaxIdentificationNumber_01a05334-190b-700d-93bf-980fba9a8408" 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_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_EntityTaxIdentificationNumber_01a05334-190b-700d-93bf-980fba9a8408" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityFileNumber_01a05334-190b-7aec-b455-5fe1f9be78ac" 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_01a05334-190b-73c1-b497-c6a1a83d8888" xlink:to="loc_dei_EntityFileNumber_01a05334-190b-7aec-b455-5fe1f9be78ac" xlink:type="arc" order="12"/>
  </link:definitionLink>
</link:linkbase>
