<?xml version="1.0" encoding="US-ASCII"?>
<!--XBRL Document Created with Wdesk from Workiva-->
<!-- -->
<link:linkbase xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/BusinessRiskAndCreditRiskConcentrationInvolvingCash" xlink:href="astc-20170930.xsd#BusinessRiskAndCreditRiskConcentrationInvolvingCash" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/BusinessRiskAndCreditRiskConcentrationInvolvingCashDetails" xlink:href="astc-20170930.xsd#BusinessRiskAndCreditRiskConcentrationInvolvingCashDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/BusinessRiskAndCreditRiskConcentrationInvolvingCashTables" xlink:href="astc-20170930.xsd#BusinessRiskAndCreditRiskConcentrationInvolvingCashTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/CommitmentsAndContingencies" xlink:href="astc-20170930.xsd#CommitmentsAndContingencies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlans" xlink:href="astc-20170930.xsd#CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlans" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansNarrativeDetails" xlink:href="astc-20170930.xsd#CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansRestrictedStockDetails" xlink:href="astc-20170930.xsd#CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansRestrictedStockDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansStockOptionActivityDetails" xlink:href="astc-20170930.xsd#CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansStockOptionActivityDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansStockOptionsByExercisePriceDetails" xlink:href="astc-20170930.xsd#CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansStockOptionsByExercisePriceDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansTables" xlink:href="astc-20170930.xsd#CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/CondensedConsolidatedBalanceSheets" xlink:href="astc-20170930.xsd#CondensedConsolidatedBalanceSheets" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:href="astc-20170930.xsd#CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/CondensedConsolidatedStatementsOfCashFlows" xlink:href="astc-20170930.xsd#CondensedConsolidatedStatementsOfCashFlows" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/CondensedConsolidatedStatementsOfOperationsAndComprehensiveLoss" xlink:href="astc-20170930.xsd#CondensedConsolidatedStatementsOfOperationsAndComprehensiveLoss" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/DocumentAndEntityInformation" xlink:href="astc-20170930.xsd#DocumentAndEntityInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/FairValueMeasurement" xlink:href="astc-20170930.xsd#FairValueMeasurement" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/FairValueMeasurementDetails" xlink:href="astc-20170930.xsd#FairValueMeasurementDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/FairValueMeasurementTables" xlink:href="astc-20170930.xsd#FairValueMeasurementTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/GeneralInformation" xlink:href="astc-20170930.xsd#GeneralInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/GeneralInformationDetails" xlink:href="astc-20170930.xsd#GeneralInformationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/GeneralInformationPolicies" xlink:href="astc-20170930.xsd#GeneralInformationPolicies" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/GoingConcernDetails" xlink:href="astc-20170930.xsd#GoingConcernDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/GoingConcernGoingConcern" xlink:href="astc-20170930.xsd#GoingConcernGoingConcern" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/IncomeTaxes" xlink:href="astc-20170930.xsd#IncomeTaxes" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/IncomeTaxesDetails" xlink:href="astc-20170930.xsd#IncomeTaxesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/Inventory" xlink:href="astc-20170930.xsd#Inventory" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/InventoryDetails" xlink:href="astc-20170930.xsd#InventoryDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/InventoryTables" xlink:href="astc-20170930.xsd#InventoryTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/Investments" xlink:href="astc-20170930.xsd#Investments" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/InvestmentsAvailableForSaleSecuritiesDetails" xlink:href="astc-20170930.xsd#InvestmentsAvailableForSaleSecuritiesDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/InvestmentsCarryingValueDetails" xlink:href="astc-20170930.xsd#InvestmentsCarryingValueDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/InvestmentsTables" xlink:href="astc-20170930.xsd#InvestmentsTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/NetLossPerShare" xlink:href="astc-20170930.xsd#NetLossPerShare" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/NetLossPerShareBasicAndDilutedComputationDetails" xlink:href="astc-20170930.xsd#NetLossPerShareBasicAndDilutedComputationDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/NetLossPerShareNarrativeDetails" xlink:href="astc-20170930.xsd#NetLossPerShareNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/NetLossPerShareTables" xlink:href="astc-20170930.xsd#NetLossPerShareTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/NoncontrollingInterest" xlink:href="astc-20170930.xsd#NoncontrollingInterest" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/NoncontrollingInterestChangesInEquityDetails" xlink:href="astc-20170930.xsd#NoncontrollingInterestChangesInEquityDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/NoncontrollingInterestContributionsDetails" xlink:href="astc-20170930.xsd#NoncontrollingInterestContributionsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/NoncontrollingInterestNarrativeDetails" xlink:href="astc-20170930.xsd#NoncontrollingInterestNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/NoncontrollingInterestTables" xlink:href="astc-20170930.xsd#NoncontrollingInterestTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/OtherComprehensiveLoss" xlink:href="astc-20170930.xsd#OtherComprehensiveLoss" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/OtherComprehensiveLossDetails" xlink:href="astc-20170930.xsd#OtherComprehensiveLossDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/OtherComprehensiveLossTables" xlink:href="astc-20170930.xsd#OtherComprehensiveLossTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/RevenueRecognition" xlink:href="astc-20170930.xsd#RevenueRecognition" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/RevenueRecognitionDetails" xlink:href="astc-20170930.xsd#RevenueRecognitionDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/SegmentInformation" xlink:href="astc-20170930.xsd#SegmentInformation" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/SegmentInformationNarrativeDetails" xlink:href="astc-20170930.xsd#SegmentInformationNarrativeDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/SegmentInformationScheduleOfSegmentsDetails" xlink:href="astc-20170930.xsd#SegmentInformationScheduleOfSegmentsDetails" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/SegmentInformationTables" xlink:href="astc-20170930.xsd#SegmentInformationTables" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/SubsequentEvents" xlink:href="astc-20170930.xsd#SubsequentEvents" xlink:type="simple" />
  <link:roleRef roleURI="http://www.astrotechcorp.com/role/SubsequentEventsDetails" xlink:href="astc-20170930.xsd#SubsequentEventsDetails" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member" xlink:type="simple" />
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension" xlink:type="simple" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/BusinessRiskAndCreditRiskConcentrationInvolvingCash" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/BusinessRiskAndCreditRiskConcentrationInvolvingCashDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskLineItems" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_931F5C9ABE6B563395774FD657D1067E" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskTable" xlink:label="loc_us-gaap_ConcentrationRiskTable_29150DDFD35B7EBC327B4FD657D1A0EB" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_931F5C9ABE6B563395774FD657D1067E" xlink:to="loc_us-gaap_ConcentrationRiskTable_29150DDFD35B7EBC327B4FD657D1A0EB" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskByTypeAxis" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_D0A7C100CD707F87D9FB4FD657D1FD1D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_29150DDFD35B7EBC327B4FD657D1A0EB" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_D0A7C100CD707F87D9FB4FD657D1FD1D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_ECFDEFB1C033D7E26CFD4FD657D16967_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_D0A7C100CD707F87D9FB4FD657D1FD1D" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_ECFDEFB1C033D7E26CFD4FD657D16967_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskTypeDomain" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_ECFDEFB1C033D7E26CFD4FD657D16967" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_D0A7C100CD707F87D9FB4FD657D1FD1D" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_ECFDEFB1C033D7E26CFD4FD657D16967" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CustomerConcentrationRiskMember" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_D9662101E8FEB8B0BBC94FD657D1C15E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_ECFDEFB1C033D7E26CFD4FD657D16967" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_D9662101E8FEB8B0BBC94FD657D1C15E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MajorCustomersAxis" xlink:label="loc_us-gaap_MajorCustomersAxis_0CE1A4FD197E05A349924FD657D11AC7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_29150DDFD35B7EBC327B4FD657D1A0EB" xlink:to="loc_us-gaap_MajorCustomersAxis_0CE1A4FD197E05A349924FD657D11AC7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NameOfMajorCustomerDomain" xlink:label="loc_us-gaap_NameOfMajorCustomerDomain_6D03973F65F0D8BAB0AE4FD657D1B271_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MajorCustomersAxis_0CE1A4FD197E05A349924FD657D11AC7" xlink:to="loc_us-gaap_NameOfMajorCustomerDomain_6D03973F65F0D8BAB0AE4FD657D1B271_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NameOfMajorCustomerDomain" xlink:label="loc_us-gaap_NameOfMajorCustomerDomain_6D03973F65F0D8BAB0AE4FD657D1B271" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MajorCustomersAxis_0CE1A4FD197E05A349924FD657D11AC7" xlink:to="loc_us-gaap_NameOfMajorCustomerDomain_6D03973F65F0D8BAB0AE4FD657D1B271" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_NGCDPartnerMember" xlink:label="loc_astc_NGCDPartnerMember_BA9D4243313264C9731F4FD657D16B21" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NameOfMajorCustomerDomain_6D03973F65F0D8BAB0AE4FD657D1B271" xlink:to="loc_astc_NGCDPartnerMember_BA9D4243313264C9731F4FD657D16B21" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_DHSSTPartnerMember" xlink:label="loc_astc_DHSSTPartnerMember_3E6630E60646F36B0A2F4FD657D192F7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NameOfMajorCustomerDomain_6D03973F65F0D8BAB0AE4FD657D1B271" xlink:to="loc_astc_DHSSTPartnerMember_3E6630E60646F36B0A2F4FD657D192F7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_1AE3459DD70472AFFE2C4FD657D15AF6" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_29150DDFD35B7EBC327B4FD657D1A0EB" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_1AE3459DD70472AFFE2C4FD657D15AF6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_D216A28B5FC12397E1F84FD657D11BF8_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_1AE3459DD70472AFFE2C4FD657D15AF6" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_D216A28B5FC12397E1F84FD657D11BF8_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskBenchmarkDomain" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_D216A28B5FC12397E1F84FD657D11BF8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_1AE3459DD70472AFFE2C4FD657D15AF6" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_D216A28B5FC12397E1F84FD657D11BF8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SalesRevenueNetMember" xlink:label="loc_us-gaap_SalesRevenueNetMember_A4595B6699303880B8E04FD657D1E768" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_D216A28B5FC12397E1F84FD657D11BF8" xlink:to="loc_us-gaap_SalesRevenueNetMember_A4595B6699303880B8E04FD657D1E768" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccountsReceivableMember" xlink:label="loc_us-gaap_AccountsReceivableMember_681DB536270586E9407A4FD657D16B82" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_D216A28B5FC12397E1F84FD657D11BF8" xlink:to="loc_us-gaap_AccountsReceivableMember_681DB536270586E9407A4FD657D16B82" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConcentrationRiskPercentage1" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_E73A80DD70255D1D2F4C4FD657D7D151" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_931F5C9ABE6B563395774FD657D1067E" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_E73A80DD70255D1D2F4C4FD657D7D151" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/BusinessRiskAndCreditRiskConcentrationInvolvingCashTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/CommitmentsAndContingencies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlans" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E0E76EC13C32215E76134A23B9849A07" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_19B6A094E754FC9AF30C4A23B983C2E5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E0E76EC13C32215E76134A23B9849A07" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_19B6A094E754FC9AF30C4A23B983C2E5" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameAxis" xlink:label="loc_us-gaap_PlanNameAxis_F9D3D7A8222CB0191F8C4A23B983243B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_19B6A094E754FC9AF30C4A23B983C2E5" xlink:to="loc_us-gaap_PlanNameAxis_F9D3D7A8222CB0191F8C4A23B983243B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_6CA27B030F7987A4D9F14A23B983890E_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_F9D3D7A8222CB0191F8C4A23B983243B" xlink:to="loc_us-gaap_PlanNameDomain_6CA27B030F7987A4D9F14A23B983890E_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PlanNameDomain" xlink:label="loc_us-gaap_PlanNameDomain_6CA27B030F7987A4D9F14A23B983890E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_F9D3D7A8222CB0191F8C4A23B983243B" xlink:to="loc_us-gaap_PlanNameDomain_6CA27B030F7987A4D9F14A23B983890E" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_SecuritiesRepurchaseProgramMember" xlink:label="loc_astc_SecuritiesRepurchaseProgramMember_4CDF4536772D4D27D9E44A23B9834599" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_6CA27B030F7987A4D9F14A23B983890E" xlink:to="loc_astc_SecuritiesRepurchaseProgramMember_4CDF4536772D4D27D9E44A23B9834599" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_DB91E77BF86EE7CBE9AB4A23B98451D2" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_19B6A094E754FC9AF30C4A23B983C2E5" xlink:to="loc_us-gaap_AwardTypeAxis_DB91E77BF86EE7CBE9AB4A23B98451D2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9D657BEB3C08EEF98CF14A23B984670C_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_DB91E77BF86EE7CBE9AB4A23B98451D2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9D657BEB3C08EEF98CF14A23B984670C_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9D657BEB3C08EEF98CF14A23B984670C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_DB91E77BF86EE7CBE9AB4A23B98451D2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9D657BEB3C08EEF98CF14A23B984670C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeStockOptionMember" xlink:label="loc_us-gaap_EmployeeStockOptionMember_1D6D6D1C0088DD42AEE74A23B984D11F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9D657BEB3C08EEF98CF14A23B984670C" xlink:to="loc_us-gaap_EmployeeStockOptionMember_1D6D6D1C0088DD42AEE74A23B984D11F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_4965B09575D786CAA42C4A23B98415CA" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_9D657BEB3C08EEF98CF14A23B984670C" xlink:to="loc_us-gaap_RestrictedStockMember_4965B09575D786CAA42C4A23B98415CA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_A8C7688DBAF8BBB33EF64A23B984C44D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E0E76EC13C32215E76134A23B9849A07" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1_A8C7688DBAF8BBB33EF64A23B984C44D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_B23EF5A25F05BBE6998F4A23B9849CB9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E0E76EC13C32215E76134A23B9849A07" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedStockOptions_B23EF5A25F05BBE6998F4A23B9849CB9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_4D181FAB609807C98E9B4A23B984170A" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E0E76EC13C32215E76134A23B9849A07" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedPeriodForRecognition1_4D181FAB609807C98E9B4A23B984170A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AllocatedShareBasedCompensationExpense" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_9B53F617303890014B7B4A23B9841F11" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E0E76EC13C32215E76134A23B9849A07" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_9B53F617303890014B7B4A23B9841F11" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_432FF529799E250627FA4A23B98456B4" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E0E76EC13C32215E76134A23B9849A07" xlink:to="loc_us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognizedShareBasedAwardsOtherThanOptions_432FF529799E250627FA4A23B98456B4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockRepurchaseProgramAuthorizedAmount1" xlink:label="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount1_D4BAD1DAA47B680F79984A23B984ADE3" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E0E76EC13C32215E76134A23B9849A07" xlink:to="loc_us-gaap_StockRepurchaseProgramAuthorizedAmount1_D4BAD1DAA47B680F79984A23B984ADE3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TreasuryStockSharesAcquired" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_AD1F2F92BFD4B0D05B9B4A23B984E2EA" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E0E76EC13C32215E76134A23B9849A07" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_AD1F2F92BFD4B0D05B9B4A23B984E2EA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_0A2B1604BCDBDDD718D94A23B985D98D" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E0E76EC13C32215E76134A23B9849A07" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_0A2B1604BCDBDDD718D94A23B985D98D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_TreasuryStockAcquiredAverageCostPerShare" xlink:label="loc_us-gaap_TreasuryStockAcquiredAverageCostPerShare_BABED0A71DA7116C52844A23B985E7AF" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_E0E76EC13C32215E76134A23B9849A07" xlink:to="loc_us-gaap_TreasuryStockAcquiredAverageCostPerShare_BABED0A71DA7116C52844A23B985E7AF" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansRestrictedStockDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_27E1781F95283BBFDED89E0DCFBBD7F6" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_AB4E075297367B4638CE9E0DCFBA230F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_27E1781F95283BBFDED89E0DCFBBD7F6" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_AB4E075297367B4638CE9E0DCFBA230F" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AwardTypeAxis" xlink:label="loc_us-gaap_AwardTypeAxis_8FB313224C32464569229E0DCFBA6E4C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_AB4E075297367B4638CE9E0DCFBA230F" xlink:to="loc_us-gaap_AwardTypeAxis_8FB313224C32464569229E0DCFBA6E4C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_DF33C8C7811706F419229E0DCFBA0C35_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_8FB313224C32464569229E0DCFBA6E4C" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_DF33C8C7811706F419229E0DCFBA0C35_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_DF33C8C7811706F419229E0DCFBA0C35" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_8FB313224C32464569229E0DCFBA6E4C" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_DF33C8C7811706F419229E0DCFBA0C35" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RestrictedStockMember" xlink:label="loc_us-gaap_RestrictedStockMember_61CA0419A77213AA51269E0DCFBA99C3" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_DF33C8C7811706F419229E0DCFBA0C35" xlink:to="loc_us-gaap_RestrictedStockMember_61CA0419A77213AA51269E0DCFBA99C3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_804D56B430A1289592399E0DCFBB9FB9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_27E1781F95283BBFDED89E0DCFBBD7F6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_804D56B430A1289592399E0DCFBB9FB9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_A600F9D2918E8217A0B19E0DCFBBDEF9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_804D56B430A1289592399E0DCFBB9FB9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_A600F9D2918E8217A0B19E0DCFBBDEF9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_91FD0340F45E07890C829E0DCFBBE7EE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_804D56B430A1289592399E0DCFBB9FB9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_91FD0340F45E07890C829E0DCFBBE7EE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_5ECE5BD5159073F9530B9E0DCFBB6CC3" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_804D56B430A1289592399E0DCFBB9FB9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_5ECE5BD5159073F9530B9E0DCFBB6CC3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_3BE8342D70016F5E95189E0DCFBB3AE9" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_804D56B430A1289592399E0DCFBB9FB9" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_3BE8342D70016F5E95189E0DCFBB3AE9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_75519022379AFF97778D9E0DCFBB6B0B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_27E1781F95283BBFDED89E0DCFBBD7F6" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_75519022379AFF97778D9E0DCFBB6B0B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_BE41E7C2CE15C6ECEA799E0DCFBBD258" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_75519022379AFF97778D9E0DCFBB6B0B" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_BE41E7C2CE15C6ECEA799E0DCFBBD258" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_EE876DF393EDEC5BE3569E0DCFBB2A43" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_75519022379AFF97778D9E0DCFBB6B0B" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_EE876DF393EDEC5BE3569E0DCFBB2A43" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_D4C77042ED57347891C19E0DCFBB4AFE" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_75519022379AFF97778D9E0DCFBB6B0B" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_D4C77042ED57347891C19E0DCFBB4AFE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_FBE2CEF6E4E3ADB5629C9E0DCFBBA6F2" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_75519022379AFF97778D9E0DCFBB6B0B" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_FBE2CEF6E4E3ADB5629C9E0DCFBBA6F2" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansStockOptionActivityDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansStockOptionsByExercisePriceDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_61D1889B956EEC809BCE4FD657A623DB" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_4FFF60CF99FB648350914FD657A6B750" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_61D1889B956EEC809BCE4FD657A623DB" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_4FFF60CF99FB648350914FD657A6B750" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_9F18B863B520AE5B67B74FD657A6C048" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeTable_4FFF60CF99FB648350914FD657A6B750" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_9F18B863B520AE5B67B74FD657A6C048" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_5FE872BEA83B3E5DADAD4FD657A6EA02_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_9F18B863B520AE5B67B74FD657A6C048" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_5FE872BEA83B3E5DADAD4FD657A6EA02_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_5FE872BEA83B3E5DADAD4FD657A6EA02" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis_9F18B863B520AE5B67B74FD657A6C048" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_5FE872BEA83B3E5DADAD4FD657A6EA02" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_ExercisePriceRangeOneMember" xlink:label="loc_astc_ExercisePriceRangeOneMember_0A00AF06B0854C3E8ABE4FD657A6A3C7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_5FE872BEA83B3E5DADAD4FD657A6EA02" xlink:to="loc_astc_ExercisePriceRangeOneMember_0A00AF06B0854C3E8ABE4FD657A6A3C7" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_ExercisePriceRangeTwoMember" xlink:label="loc_astc_ExercisePriceRangeTwoMember_BA5A2214F88D43678A114FD657A653A9" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_5FE872BEA83B3E5DADAD4FD657A6EA02" xlink:to="loc_astc_ExercisePriceRangeTwoMember_BA5A2214F88D43678A114FD657A653A9" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_ExercisePriceRangeThreeMember" xlink:label="loc_astc_ExercisePriceRangeThreeMember_BFE8FB524CF7DE6EE9B84FD657A6DDC9" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeDomain_5FE872BEA83B3E5DADAD4FD657A6EA02" xlink:to="loc_astc_ExercisePriceRangeThreeMember_BFE8FB524CF7DE6EE9B84FD657A6DDC9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_E926B2A080484AAD4FDF4FD657A69DA8" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_61D1889B956EEC809BCE4FD657A623DB" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit_E926B2A080484AAD4FDF4FD657A69DA8" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_A410AAA80E6F2A4D39084FD657A652A3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_61D1889B956EEC809BCE4FD657A623DB" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit_A410AAA80E6F2A4D39084FD657A652A3" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_0F40B9A1185C69EEEA8F4FD657A61A73" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_61D1889B956EEC809BCE4FD657A623DB" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions_0F40B9A1185C69EEEA8F4FD657A61A73" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_6569ACEA60CDF24901634FD657A68BEF" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_61D1889B956EEC809BCE4FD657A623DB" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageRemainingContractualTerm2_6569ACEA60CDF24901634FD657A68BEF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1_280C48A007FE47A1513A4FD657A69754" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_61D1889B956EEC809BCE4FD657A623DB" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeOutstandingOptionsWeightedAverageExercisePriceBeginningBalance1_280C48A007FE47A1513A4FD657A69754" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions" xlink:label="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions_4B08167597E5D6C479104FD657A6C301" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_61D1889B956EEC809BCE4FD657A623DB" xlink:to="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions_4B08167597E5D6C479104FD657A6C301" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1" xlink:label="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1_6BC684B3A016696FEC8D4FD657A7C4CA" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems_61D1889B956EEC809BCE4FD657A623DB" xlink:to="loc_us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1_6BC684B3A016696FEC8D4FD657A7C4CA" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/CommonStockIncentiveStockPurchasePlansAndOtherCompensationPlansTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/CondensedConsolidatedBalanceSheets" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/CondensedConsolidatedBalanceSheetsParenthetical" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/CondensedConsolidatedStatementsOfCashFlows" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/CondensedConsolidatedStatementsOfOperationsAndComprehensiveLoss" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/DocumentAndEntityInformation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/FairValueMeasurement" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/FairValueMeasurementDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByBalanceSheetGroupingTable" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_648C8BD8AEBB30BA118D9E0DCFDB2C74" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_648C8BD8AEBB30BA118D9E0DCFDB2C74" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_814DCBDAAEC12BC18F139E0DCFDB4759" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_648C8BD8AEBB30BA118D9E0DCFDB2C74" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_814DCBDAAEC12BC18F139E0DCFDB4759" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_F47B39AD13AE7B47D8EC9E0DCFDBE9DA_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_814DCBDAAEC12BC18F139E0DCFDB4759" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_F47B39AD13AE7B47D8EC9E0DCFDBE9DA_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_F47B39AD13AE7B47D8EC9E0DCFDBE9DA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_814DCBDAAEC12BC18F139E0DCFDB4759" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_F47B39AD13AE7B47D8EC9E0DCFDBE9DA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel1Member" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_E00FADA877127A03820B9E0DCFDBA622" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_F47B39AD13AE7B47D8EC9E0DCFDBE9DA" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_E00FADA877127A03820B9E0DCFDBA622" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel2Member" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_F98F3A20683E5B2BE1A09E0DCFDC0FB7" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_F47B39AD13AE7B47D8EC9E0DCFDBE9DA" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_F98F3A20683E5B2BE1A09E0DCFDC0FB7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FairValueInputsLevel3Member" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_12F7714BDFC010C176CD9E0DCFDC5D57" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_F47B39AD13AE7B47D8EC9E0DCFDBE9DA" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_12F7714BDFC010C176CD9E0DCFDC5D57" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_MutualFundsCarringValue" xlink:label="loc_astc_MutualFundsCarringValue_70143E64A7ADD8AFDC6F9E0DCFDCDFD2" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:to="loc_astc_MutualFundsCarringValue_70143E64A7ADD8AFDC6F9E0DCFDCDFD2" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_MutualFundsFairValue" xlink:label="loc_astc_MutualFundsFairValue_2B16E484EDACF6ECBDAD9E0DCFDC076E" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:to="loc_astc_MutualFundsFairValue_2B16E484EDACF6ECBDAD9E0DCFDC076E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount_B85FA61FB3BA36DCF49C9E0DCFDCF2C2" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount_B85FA61FB3BA36DCF49C9E0DCFDCF2C2" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue_664B6DB9F00413D7BFF99E0DCFDCCB21" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearFairValue_664B6DB9F00413D7BFF99E0DCFDCCB21" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_HeldtomaturitySecuritiesDebtMaturitiesafterOneThroughThreeYearsNetCarryingAmount" xlink:label="loc_astc_HeldtomaturitySecuritiesDebtMaturitiesafterOneThroughThreeYearsNetCarryingAmount_65159D508DA5C04FCEE09E0DCFDCCC2E" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:to="loc_astc_HeldtomaturitySecuritiesDebtMaturitiesafterOneThroughThreeYearsNetCarryingAmount_65159D508DA5C04FCEE09E0DCFDCCC2E" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_HeldtomaturitySecuritiesDebtMaturitiesafterOneThroughThreeYearsFairValue" xlink:label="loc_astc_HeldtomaturitySecuritiesDebtMaturitiesafterOneThroughThreeYearsFairValue_6095FF3487D1CADC841A9E0DCFDC0D49" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:to="loc_astc_HeldtomaturitySecuritiesDebtMaturitiesafterOneThroughThreeYearsFairValue_6095FF3487D1CADC841A9E0DCFDC0D49" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_HeldToMaturitySecuritiesDebtMaturities91To360DaysNetCarryingAmount" xlink:label="loc_astc_HeldToMaturitySecuritiesDebtMaturities91To360DaysNetCarryingAmount_8D6A94E0BDD70303A16B9E0DCFDC15AB" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:to="loc_astc_HeldToMaturitySecuritiesDebtMaturities91To360DaysNetCarryingAmount_8D6A94E0BDD70303A16B9E0DCFDC15AB" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_HeldToMaturitySecuritiesDebtMaturities91To360DaysFairValue" xlink:label="loc_astc_HeldToMaturitySecuritiesDebtMaturities91To360DaysFairValue_7CC3AE53C66C7107C2569E0DCFDCB450" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:to="loc_astc_HeldToMaturitySecuritiesDebtMaturities91To360DaysFairValue_7CC3AE53C66C7107C2569E0DCFDCB450" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_HeldToMaturitySecuritiesDebtMaturitiesOver360DaysNetCarryingAmount" xlink:label="loc_astc_HeldToMaturitySecuritiesDebtMaturitiesOver360DaysNetCarryingAmount_6F25703999EEC704949E9E0DCFDC65D3" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:to="loc_astc_HeldToMaturitySecuritiesDebtMaturitiesOver360DaysNetCarryingAmount_6F25703999EEC704949E9E0DCFDC65D3" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_HeldToMaturitySecuritiesDebtMaturitiesOver360DaysFairValue" xlink:label="loc_astc_HeldToMaturitySecuritiesDebtMaturitiesOver360DaysFairValue_258F8B96C74FCE6F47B89E0DCFDCD87C" xlink:type="locator" />
    <link:definitionArc order="10" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:to="loc_astc_HeldToMaturitySecuritiesDebtMaturitiesOver360DaysFairValue_258F8B96C74FCE6F47B89E0DCFDCD87C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Investments" xlink:label="loc_us-gaap_Investments_9A7A9352D99A00BF5A3C9E0DCFDC289C" xlink:type="locator" />
    <link:definitionArc order="11" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:to="loc_us-gaap_Investments_9A7A9352D99A00BF5A3C9E0DCFDC289C" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentsFairValueDisclosure" xlink:label="loc_us-gaap_InvestmentsFairValueDisclosure_37126215D502CD2EEB879E0DCFDC6E97" xlink:type="locator" />
    <link:definitionArc order="12" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems_B5C437A8F57381570B1A9E0DCFDC5F10" xlink:to="loc_us-gaap_InvestmentsFairValueDisclosure_37126215D502CD2EEB879E0DCFDC6E97" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/FairValueMeasurementTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/GeneralInformation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/GeneralInformationDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventLineItems" xlink:label="loc_us-gaap_SubsequentEventLineItems_D21D9FBBEC8921DC88839E0DD013502F" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTable" xlink:label="loc_us-gaap_SubsequentEventTable_1874576154A87408A4E79E0DD0132601" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_D21D9FBBEC8921DC88839E0DD013502F" xlink:to="loc_us-gaap_SubsequentEventTable_1874576154A87408A4E79E0DD0132601" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_72C1C935CFAC7F037D669E0DD013F2E5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_1874576154A87408A4E79E0DD0132601" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_72C1C935CFAC7F037D669E0DD013F2E5" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_B30DE9CBEA0F10D03EFF9E0DD0136266_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_72C1C935CFAC7F037D669E0DD013F2E5" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_B30DE9CBEA0F10D03EFF9E0DD0136266_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_B30DE9CBEA0F10D03EFF9E0DD0136266" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_72C1C935CFAC7F037D669E0DD013F2E5" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_B30DE9CBEA0F10D03EFF9E0DD0136266" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember_C612ECF9CFADE3F90E859E0DD013C102" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_B30DE9CBEA0F10D03EFF9E0DD0136266" xlink:to="loc_us-gaap_SubsequentEventMember_C612ECF9CFADE3F90E859E0DD013C102" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_92D4B64B8CD248A4D93C9E176300E909" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_D21D9FBBEC8921DC88839E0DD013502F" xlink:to="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_92D4B64B8CD248A4D93C9E176300E909" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CommonStockSharesAuthorized" xlink:label="loc_us-gaap_CommonStockSharesAuthorized_98F2E2E0219CBAB9BA859E0DD013D2DB" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_D21D9FBBEC8921DC88839E0DD013502F" xlink:to="loc_us-gaap_CommonStockSharesAuthorized_98F2E2E0219CBAB9BA859E0DD013D2DB" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/GeneralInformationPolicies" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/GoingConcernDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/GoingConcernGoingConcern" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/IncomeTaxes" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/IncomeTaxesDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/Inventory" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/InventoryDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/InventoryTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/Investments" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/InvestmentsAvailableForSaleSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_InvestmentLineItems" xlink:label="loc_invest_InvestmentLineItems_1F6933A67E470ABAACE14A23B9E2D542" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.sec.gov/invest/2013/invest-2013-01-31.xsd#invest_InvestmentTable" xlink:label="loc_invest_InvestmentTable_047ABBD5A19D35FFD8924A23B9E2B870" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_invest_InvestmentLineItems_1F6933A67E470ABAACE14A23B9E2D542" xlink:to="loc_invest_InvestmentTable_047ABBD5A19D35FFD8924A23B9E2B870" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentTypeAxis" xlink:label="loc_us-gaap_InvestmentTypeAxis_B5D736C8265B1D9213BD4A23B9E25BB0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_invest_InvestmentTable_047ABBD5A19D35FFD8924A23B9E2B870" xlink:to="loc_us-gaap_InvestmentTypeAxis_B5D736C8265B1D9213BD4A23B9E25BB0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_133BF4503A3EE35D6A104A23B9E2A585_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_B5D736C8265B1D9213BD4A23B9E25BB0" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_133BF4503A3EE35D6A104A23B9E2A585_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_133BF4503A3EE35D6A104A23B9E2A585" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_B5D736C8265B1D9213BD4A23B9E25BB0" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_133BF4503A3EE35D6A104A23B9E2A585" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_MutualFundsMember" xlink:label="loc_astc_MutualFundsMember_CA98D7DDF574D7BE2A2A4A23B9E2F374" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_133BF4503A3EE35D6A104A23B9E2A585" xlink:to="loc_astc_MutualFundsMember_CA98D7DDF574D7BE2A2A4A23B9E2F374" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FixedIncomeInvestmentsMember" xlink:label="loc_us-gaap_FixedIncomeInvestmentsMember_9FECD9893A4992A1887E4A23B9E237C1" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_133BF4503A3EE35D6A104A23B9E2A585" xlink:to="loc_us-gaap_FixedIncomeInvestmentsMember_9FECD9893A4992A1887E4A23B9E237C1" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BankTimeDepositsMember" xlink:label="loc_us-gaap_BankTimeDepositsMember_D12EC3E06E37120F500F4A23B9E2C8E9" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_133BF4503A3EE35D6A104A23B9E2A585" xlink:to="loc_us-gaap_BankTimeDepositsMember_D12EC3E06E37120F500F4A23B9E2C8E9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAbstract" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesAbstract_7CE5F105B9683DAF54954A23B9E2D938" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_invest_InvestmentLineItems_1F6933A67E470ABAACE14A23B9E2D542" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesAbstract_7CE5F105B9683DAF54954A23B9E2D938" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAmortizedCost" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesAmortizedCost_966D8F0489ACA669F41A4A23B9E3745F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesAbstract_7CE5F105B9683DAF54954A23B9E2D938" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesAmortizedCost_966D8F0489ACA669F41A4A23B9E3745F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_099B825BC550AE64BC2A4A23B9E3FA89" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesAbstract_7CE5F105B9683DAF54954A23B9E2D938" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_099B825BC550AE64BC2A4A23B9E3FA89" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_90BCF7BA3F671BD6642B4A23B9E31102" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesAbstract_7CE5F105B9683DAF54954A23B9E2D938" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_90BCF7BA3F671BD6642B4A23B9E31102" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecurities" xlink:label="loc_us-gaap_AvailableForSaleSecurities_0E35A69BBC5FB65FA4B84A23B9E37095" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AvailableForSaleSecuritiesAbstract_7CE5F105B9683DAF54954A23B9E2D938" xlink:to="loc_us-gaap_AvailableForSaleSecurities_0E35A69BBC5FB65FA4B84A23B9E37095" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/InvestmentsCarryingValueDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems" xlink:label="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_28C5E247D3ED400ADF894FD6587C4FE6" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfHeldToMaturitySecuritiesTable" xlink:label="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesTable_63AB08FEA619DF3A61DC4FD6587B5F19" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_28C5E247D3ED400ADF894FD6587C4FE6" xlink:to="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesTable_63AB08FEA619DF3A61DC4FD6587B5F19" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentTypeAxis" xlink:label="loc_us-gaap_InvestmentTypeAxis_9C7925559B96643CA82A4FD6587BEF6B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesTable_63AB08FEA619DF3A61DC4FD6587B5F19" xlink:to="loc_us-gaap_InvestmentTypeAxis_9C7925559B96643CA82A4FD6587BEF6B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_B74C9BD349A043B97FD94FD6587B165D_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_InvestmentTypeAxis_9C7925559B96643CA82A4FD6587BEF6B" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_B74C9BD349A043B97FD94FD6587B165D_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_InvestmentTypeCategorizationMember" xlink:label="loc_us-gaap_InvestmentTypeCategorizationMember_B74C9BD349A043B97FD94FD6587B165D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_InvestmentTypeAxis_9C7925559B96643CA82A4FD6587BEF6B" xlink:to="loc_us-gaap_InvestmentTypeCategorizationMember_B74C9BD349A043B97FD94FD6587B165D" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_MutualFundsMember" xlink:label="loc_astc_MutualFundsMember_2CEE592016F56596B0FA4FD6587BDDE7" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_B74C9BD349A043B97FD94FD6587B165D" xlink:to="loc_astc_MutualFundsMember_2CEE592016F56596B0FA4FD6587BDDE7" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BankTimeDepositsMember" xlink:label="loc_us-gaap_BankTimeDepositsMember_5AA7513A6C4CAA9809284FD6587B920B" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_B74C9BD349A043B97FD94FD6587B165D" xlink:to="loc_us-gaap_BankTimeDepositsMember_5AA7513A6C4CAA9809284FD6587B920B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_FixedIncomeInvestmentsMember" xlink:label="loc_us-gaap_FixedIncomeInvestmentsMember_32576693CAF7993BC8F44FD6587B0392" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_InvestmentTypeCategorizationMember_B74C9BD349A043B97FD94FD6587B165D" xlink:to="loc_us-gaap_FixedIncomeInvestmentsMember_32576693CAF7993BC8F44FD6587B0392" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationAxis" xlink:label="loc_us-gaap_BalanceSheetLocationAxis_F259C8D6D539272E24C84FD6587B9A29" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesTable_63AB08FEA619DF3A61DC4FD6587B5F19" xlink:to="loc_us-gaap_BalanceSheetLocationAxis_F259C8D6D539272E24C84FD6587B9A29" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_0501D94D4020AE60F16E4FD6587B88A6_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_F259C8D6D539272E24C84FD6587B9A29" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_0501D94D4020AE60F16E4FD6587B88A6_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_BalanceSheetLocationDomain" xlink:label="loc_us-gaap_BalanceSheetLocationDomain_0501D94D4020AE60F16E4FD6587B88A6" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BalanceSheetLocationAxis_F259C8D6D539272E24C84FD6587B9A29" xlink:to="loc_us-gaap_BalanceSheetLocationDomain_0501D94D4020AE60F16E4FD6587B88A6" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ShortTermInvestmentsMember" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_9D7A1016EDEBD92AC16C4FD6587CE98E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_0501D94D4020AE60F16E4FD6587B88A6" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_9D7A1016EDEBD92AC16C4FD6587CE98E" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_LongTermInvestmentsMember" xlink:label="loc_astc_LongTermInvestmentsMember_77FCAD3DF90201B535F14FD6587CF6C0" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BalanceSheetLocationDomain_0501D94D4020AE60F16E4FD6587B88A6" xlink:to="loc_astc_LongTermInvestmentsMember_77FCAD3DF90201B535F14FD6587CF6C0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecurities" xlink:label="loc_us-gaap_AvailableForSaleSecurities_AC91DF9AF637A90C85414FD6587C29F0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_28C5E247D3ED400ADF894FD6587C4FE6" xlink:to="loc_us-gaap_AvailableForSaleSecurities_AC91DF9AF637A90C85414FD6587C29F0" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_HeldToMaturitySecuritiesDebtMaturities1To90DaysNetCarryingAmount" xlink:label="loc_astc_HeldToMaturitySecuritiesDebtMaturities1To90DaysNetCarryingAmount_159E1D4CC82E0FC26B284FD6587C1DA3" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_28C5E247D3ED400ADF894FD6587C4FE6" xlink:to="loc_astc_HeldToMaturitySecuritiesDebtMaturities1To90DaysNetCarryingAmount_159E1D4CC82E0FC26B284FD6587C1DA3" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_HeldToMaturitySecuritiesDebtMaturities91To360DaysNetCarryingAmount" xlink:label="loc_astc_HeldToMaturitySecuritiesDebtMaturities91To360DaysNetCarryingAmount_E0BBD5EE2D5409C037D34FD6587C4A27" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_28C5E247D3ED400ADF894FD6587C4FE6" xlink:to="loc_astc_HeldToMaturitySecuritiesDebtMaturities91To360DaysNetCarryingAmount_E0BBD5EE2D5409C037D34FD6587C4A27" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount" xlink:label="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount_30A4BB8B3F7D04C4F8884FD6587CF816" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_28C5E247D3ED400ADF894FD6587C4FE6" xlink:to="loc_us-gaap_HeldToMaturitySecuritiesDebtMaturitiesWithinOneYearNetCarryingAmount_30A4BB8B3F7D04C4F8884FD6587CF816" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AvailableForSaleSecuritiesAndHeldToMaturitySecurities" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesAndHeldToMaturitySecurities_5DD255B0D0BE8D4EB7FF4FD6587C769C" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_28C5E247D3ED400ADF894FD6587C4FE6" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesAndHeldToMaturitySecurities_5DD255B0D0BE8D4EB7FF4FD6587C769C" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_HeldToMaturitySecuritiesDebtMaturitiesOver360DaysNetCarryingAmount" xlink:label="loc_astc_HeldToMaturitySecuritiesDebtMaturitiesOver360DaysNetCarryingAmount_2BB7FF144CF52DC3A6D84FD6587C11C3" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_28C5E247D3ED400ADF894FD6587C4FE6" xlink:to="loc_astc_HeldToMaturitySecuritiesDebtMaturitiesOver360DaysNetCarryingAmount_2BB7FF144CF52DC3A6D84FD6587C11C3" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_HeldtomaturitySecuritiesDebtMaturitiesafterOneThroughThreeYearsNetCarryingAmount" xlink:label="loc_astc_HeldtomaturitySecuritiesDebtMaturitiesafterOneThroughThreeYearsNetCarryingAmount_81CE8E5D4911EAC60CBA4FD6587CFFB2" xlink:type="locator" />
    <link:definitionArc order="7" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_28C5E247D3ED400ADF894FD6587C4FE6" xlink:to="loc_astc_HeldtomaturitySecuritiesDebtMaturitiesafterOneThroughThreeYearsNetCarryingAmount_81CE8E5D4911EAC60CBA4FD6587CFFB2" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_HeldtomaturitySecuritiesDebtMaturitiesafterThreeThroughFiveYearsNetCarryingAmount" xlink:label="loc_astc_HeldtomaturitySecuritiesDebtMaturitiesafterThreeThroughFiveYearsNetCarryingAmount_B9937E3347FD3490E7A14FEEA205A6AF" xlink:type="locator" />
    <link:definitionArc order="8" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_28C5E247D3ED400ADF894FD6587C4FE6" xlink:to="loc_astc_HeldtomaturitySecuritiesDebtMaturitiesafterThreeThroughFiveYearsNetCarryingAmount_B9937E3347FD3490E7A14FEEA205A6AF" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_HeldToMaturitySecurities" xlink:label="loc_us-gaap_HeldToMaturitySecurities_C2C52F4ADA83DC58F1DB4FD6587CCB06" xlink:type="locator" />
    <link:definitionArc order="9" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfHeldToMaturitySecuritiesLineItems_28C5E247D3ED400ADF894FD6587C4FE6" xlink:to="loc_us-gaap_HeldToMaturitySecurities_C2C52F4ADA83DC58F1DB4FD6587CCB06" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/InvestmentsTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/NetLossPerShare" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/NetLossPerShareBasicAndDilutedComputationDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/NetLossPerShareNarrativeDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/NetLossPerShareTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/NoncontrollingInterest" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/NoncontrollingInterestChangesInEquityDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/NoncontrollingInterestContributionsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterestLineItems" xlink:label="loc_us-gaap_MinorityInterestLineItems_949F8B92C059BD166469264B5D506188" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterestTable" xlink:label="loc_us-gaap_MinorityInterestTable_422BBF5A9EBC0F2068F2264B5D4FC827" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MinorityInterestLineItems_949F8B92C059BD166469264B5D506188" xlink:to="loc_us-gaap_MinorityInterestTable_422BBF5A9EBC0F2068F2264B5D4FC827" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesAxis" xlink:label="loc_us-gaap_ConsolidatedEntitiesAxis_B32B540354D8EF04FF87264C172BD71A" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MinorityInterestTable_422BBF5A9EBC0F2068F2264B5D4FC827" xlink:to="loc_us-gaap_ConsolidatedEntitiesAxis_B32B540354D8EF04FF87264C172BD71A" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="loc_us-gaap_ConsolidatedEntitiesDomain_5F4027D8693C28A6C729264C172C0129_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConsolidatedEntitiesAxis_B32B540354D8EF04FF87264C172BD71A" xlink:to="loc_us-gaap_ConsolidatedEntitiesDomain_5F4027D8693C28A6C729264C172C0129_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ConsolidatedEntitiesDomain" xlink:label="loc_us-gaap_ConsolidatedEntitiesDomain_5F4027D8693C28A6C729264C172C0129" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConsolidatedEntitiesAxis_B32B540354D8EF04FF87264C172BD71A" xlink:to="loc_us-gaap_ConsolidatedEntitiesDomain_5F4027D8693C28A6C729264C172C0129" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ParentCompanyMember" xlink:label="loc_us-gaap_ParentCompanyMember_93CBE4090166FA9E1E57264B5D50CB7F" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_5F4027D8693C28A6C729264C172C0129" xlink:to="loc_us-gaap_ParentCompanyMember_93CBE4090166FA9E1E57264B5D50CB7F" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsidiariesMember" xlink:label="loc_us-gaap_SubsidiariesMember_74099DD21B47AC95E498264B5D503EEE" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConsolidatedEntitiesDomain_5F4027D8693C28A6C729264C172C0129" xlink:to="loc_us-gaap_SubsidiariesMember_74099DD21B47AC95E498264B5D503EEE" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance" xlink:label="loc_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance_F9DDF1384C3880398B77264B5D5048E4" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_949F8B92C059BD166469264B5D506188" xlink:to="loc_us-gaap_NoncontrollingInterestIncreaseFromSubsidiaryEquityIssuance_F9DDF1384C3880398B77264B5D5048E4" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_25D4DFE622A0DC302E2E264B5D50629D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_949F8B92C059BD166469264B5D506188" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_25D4DFE622A0DC302E2E264B5D50629D" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/NoncontrollingInterestNarrativeDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterestLineItems" xlink:label="loc_us-gaap_MinorityInterestLineItems_73941351AF2AA0ACE407264B5D53C512" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterestTable" xlink:label="loc_us-gaap_MinorityInterestTable_3A51DAB26FE360EF334D264B5D5254A0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_MinorityInterestLineItems_73941351AF2AA0ACE407264B5D53C512" xlink:to="loc_us-gaap_MinorityInterestTable_3A51DAB26FE360EF334D264B5D5254A0" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_CounterpartyNameAxis" xlink:label="loc_us-gaap_CounterpartyNameAxis_BA10E2F1070283C449B2264B5D526DB0" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_MinorityInterestTable_3A51DAB26FE360EF334D264B5D5254A0" xlink:to="loc_us-gaap_CounterpartyNameAxis_BA10E2F1070283C449B2264B5D526DB0" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_0B10054233BC6FBDFFBC264B5D52F030_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CounterpartyNameAxis_BA10E2F1070283C449B2264B5D526DB0" xlink:to="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_0B10054233BC6FBDFFBC264B5D52F030_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RepurchaseAgreementCounterpartyNameDomain" xlink:label="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_0B10054233BC6FBDFFBC264B5D52F030" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CounterpartyNameAxis_BA10E2F1070283C449B2264B5D526DB0" xlink:to="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_0B10054233BC6FBDFFBC264B5D52F030" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_AstralImagesIncMember" xlink:label="loc_astc_AstralImagesIncMember_31C22A4BD417523E04F3264B5D53EC36" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RepurchaseAgreementCounterpartyNameDomain_0B10054233BC6FBDFFBC264B5D52F030" xlink:to="loc_astc_AstralImagesIncMember_31C22A4BD417523E04F3264B5D53EC36" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinorityInterestOwnershipPercentageByParent" xlink:label="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_FAC860F3311EE147D162264B5D53F338" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MinorityInterestLineItems_73941351AF2AA0ACE407264B5D53C512" xlink:to="loc_us-gaap_MinorityInterestOwnershipPercentageByParent_FAC860F3311EE147D162264B5D53F338" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/NoncontrollingInterestTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/OtherComprehensiveLoss" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/OtherComprehensiveLossDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_DE95CB5B9AD051FEA5987EE59368B479" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_FA00F51B53BAD8B5D9BB7EE593677488" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_DE95CB5B9AD051FEA5987EE59368B479" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_FA00F51B53BAD8B5D9BB7EE593677488" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementEquityComponentsAxis" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_A2B1F620ADC3D534B0777EE59367C6D9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_FA00F51B53BAD8B5D9BB7EE593677488" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_A2B1F620ADC3D534B0777EE59367C6D9" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_0C7089B154CA0CE3D94C7EE593670680_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_A2B1F620ADC3D534B0777EE59367C6D9" xlink:to="loc_us-gaap_EquityComponentDomain_0C7089B154CA0CE3D94C7EE593670680_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_EquityComponentDomain" xlink:label="loc_us-gaap_EquityComponentDomain_0C7089B154CA0CE3D94C7EE593670680" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_A2B1F620ADC3D534B0777EE59367C6D9" xlink:to="loc_us-gaap_EquityComponentDomain_0C7089B154CA0CE3D94C7EE593670680" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_0372FA473CDB462B570E7EE593680F98" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_0C7089B154CA0CE3D94C7EE593670680" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_0372FA473CDB462B570E7EE593680F98" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_258BB6B725ADFCD065C27EE593680011" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_DE95CB5B9AD051FEA5987EE59368B479" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_258BB6B725ADFCD065C27EE593680011" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest" xlink:label="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_1906BF4F33C093B4433F7EE593684B13" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_258BB6B725ADFCD065C27EE593680011" xlink:to="loc_us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest_1906BF4F33C093B4433F7EE593684B13" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_814E7F243E5F76475F1E7EE593680810" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_258BB6B725ADFCD065C27EE593680011" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsNetOfTax_814E7F243E5F76475F1E7EE593680810" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax" xlink:label="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_E14837ACE1C822D77C947EE59368EE3C" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTaxAbstract_258BB6B725ADFCD065C27EE593680011" xlink:to="loc_us-gaap_ReclassificationFromAccumulatedOtherComprehensiveIncomeCurrentPeriodNetOfTax_E14837ACE1C822D77C947EE59368EE3C" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/OtherComprehensiveLossTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/RevenueRecognition" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/RevenueRecognitionDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueRecognitionMultipleDeliverableArrangementsLineItems" xlink:label="loc_us-gaap_RevenueRecognitionMultipleDeliverableArrangementsLineItems_C616715875589E794C54264B5D2A5A45" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RevenueRecognitionMultipleDeliverableArrangementsTable" xlink:label="loc_us-gaap_RevenueRecognitionMultipleDeliverableArrangementsTable_F7B5DB519A6F4302B037264B5D294244" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_RevenueRecognitionMultipleDeliverableArrangementsLineItems_C616715875589E794C54264B5D2A5A45" xlink:to="loc_us-gaap_RevenueRecognitionMultipleDeliverableArrangementsTable_F7B5DB519A6F4302B037264B5D294244" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeAxis" xlink:label="loc_us-gaap_RangeAxis_B5FBC6A2072839DA00EF264B5D29A766" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_RevenueRecognitionMultipleDeliverableArrangementsTable_F7B5DB519A6F4302B037264B5D294244" xlink:to="loc_us-gaap_RangeAxis_B5FBC6A2072839DA00EF264B5D29A766" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_B1DE8E332F8E26C5B5FE264B5D29D681_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_RangeAxis_B5FBC6A2072839DA00EF264B5D29A766" xlink:to="loc_us-gaap_RangeMember_B1DE8E332F8E26C5B5FE264B5D29D681_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_RangeMember" xlink:label="loc_us-gaap_RangeMember_B1DE8E332F8E26C5B5FE264B5D29D681" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_RangeAxis_B5FBC6A2072839DA00EF264B5D29A766" xlink:to="loc_us-gaap_RangeMember_B1DE8E332F8E26C5B5FE264B5D29D681" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MinimumMember" xlink:label="loc_us-gaap_MinimumMember_108B144429BBEA961FEC264B5D2921CA" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_B1DE8E332F8E26C5B5FE264B5D29D681" xlink:to="loc_us-gaap_MinimumMember_108B144429BBEA961FEC264B5D2921CA" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_MaximumMember" xlink:label="loc_us-gaap_MaximumMember_A4150A6AF74ACC5008C9264B5D2A8332" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RangeMember_B1DE8E332F8E26C5B5FE264B5D29D681" xlink:to="loc_us-gaap_MaximumMember_A4150A6AF74ACC5008C9264B5D2A8332" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_RevenueRecognitionFixedPriceSubcontractOnGovernmentProjectTerm" xlink:label="loc_astc_RevenueRecognitionFixedPriceSubcontractOnGovernmentProjectTerm_26811BE565A568AB40CF264B5D2AE416" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenueRecognitionMultipleDeliverableArrangementsLineItems_C616715875589E794C54264B5D2A5A45" xlink:to="loc_astc_RevenueRecognitionFixedPriceSubcontractOnGovernmentProjectTerm_26811BE565A568AB40CF264B5D2AE416" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/SegmentInformation" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/SegmentInformationNarrativeDetails" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/SegmentInformationScheduleOfSegmentsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentReportingInformationLineItems" xlink:label="loc_us-gaap_SegmentReportingInformationLineItems_56166FCA3ED7A97F008A264B5CF94EC7" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable" xlink:label="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_238AC1ABECBA10511B8E264B5CF86AF9" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_56166FCA3ED7A97F008A264B5CF94EC7" xlink:to="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_238AC1ABECBA10511B8E264B5CF86AF9" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StatementBusinessSegmentsAxis" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_B6DAB223B3B4CB355207264B5CF8928D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfSegmentReportingInformationBySegmentTable_238AC1ABECBA10511B8E264B5CF86AF9" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_B6DAB223B3B4CB355207264B5CF8928D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_80733A8CCA4BA43A29A0264B5CF86AB5_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_B6DAB223B3B4CB355207264B5CF8928D" xlink:to="loc_us-gaap_SegmentDomain_80733A8CCA4BA43A29A0264B5CF86AB5_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SegmentDomain" xlink:label="loc_us-gaap_SegmentDomain_80733A8CCA4BA43A29A0264B5CF86AB5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_B6DAB223B3B4CB355207264B5CF8928D" xlink:to="loc_us-gaap_SegmentDomain_80733A8CCA4BA43A29A0264B5CF86AB5" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_AstroScientificMember" xlink:label="loc_astc_AstroScientificMember_FE8AB578EA1E59F24309264B5CF8C78C" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_80733A8CCA4BA43A29A0264B5CF86AB5" xlink:to="loc_astc_AstroScientificMember_FE8AB578EA1E59F24309264B5CF8C78C" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_AstralImagesIncMember" xlink:label="loc_astc_AstralImagesIncMember_A5E170948E29580F9B4D264B5CF8AC82" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_80733A8CCA4BA43A29A0264B5CF86AB5" xlink:to="loc_astc_AstralImagesIncMember_A5E170948E29580F9B4D264B5CF8AC82" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Revenues" xlink:label="loc_us-gaap_Revenues_60CDC9425CFEBC1FAC4A264B5CF9229D" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_56166FCA3ED7A97F008A264B5CF94EC7" xlink:to="loc_us-gaap_Revenues_60CDC9425CFEBC1FAC4A264B5CF9229D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_DepreciationDepletionAndAmortization" xlink:label="loc_us-gaap_DepreciationDepletionAndAmortization_6ECA292C7D19145C36C1264B5CF9BD1D" xlink:type="locator" />
    <link:definitionArc order="2" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_56166FCA3ED7A97F008A264B5CF94EC7" xlink:to="loc_us-gaap_DepreciationDepletionAndAmortization_6ECA292C7D19145C36C1264B5CF9BD1D" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_F63D208E4CE8680DA88A264B5CF9D367" xlink:type="locator" />
    <link:definitionArc order="3" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_56166FCA3ED7A97F008A264B5CF94EC7" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_F63D208E4CE8680DA88A264B5CF9D367" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_PropertyPlantAndEquipmentNet" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_E18C3B1E06FE640C6F30264B5CF9734A" xlink:type="locator" />
    <link:definitionArc order="4" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_56166FCA3ED7A97F008A264B5CF94EC7" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_E18C3B1E06FE640C6F30264B5CF9734A" xlink:type="arc" />
    <link:loc xlink:href="astc-20170930.xsd#astc_CapitalExpenditure" xlink:label="loc_astc_CapitalExpenditure_1B778C0BF02BB1AC4FFB264B5CF9325B" xlink:type="locator" />
    <link:definitionArc order="5" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_56166FCA3ED7A97F008A264B5CF94EC7" xlink:to="loc_astc_CapitalExpenditure_1B778C0BF02BB1AC4FFB264B5CF9325B" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_Assets" xlink:label="loc_us-gaap_Assets_534DD5223AB4198A6BCC264B5CF99E15" xlink:type="locator" />
    <link:definitionArc order="6" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingInformationLineItems_56166FCA3ED7A97F008A264B5CF94EC7" xlink:to="loc_us-gaap_Assets_534DD5223AB4198A6BCC264B5CF99E15" xlink:type="arc" />
  </link:definitionLink>
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/SegmentInformationTables" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/SubsequentEvents" xlink:type="extended" />
  <link:definitionLink xlink:role="http://www.astrotechcorp.com/role/SubsequentEventsDetails" xlink:type="extended">
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventLineItems" xlink:label="loc_us-gaap_SubsequentEventLineItems_EDA0E953871C6D65EB8D9E0DCF9F9E33" xlink:type="locator" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTable" xlink:label="loc_us-gaap_SubsequentEventTable_33B5871803204C960E0A9E0DCF9D9DF5" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SubsequentEventLineItems_EDA0E953871C6D65EB8D9E0DCF9F9E33" xlink:to="loc_us-gaap_SubsequentEventTable_33B5871803204C960E0A9E0DCF9D9DF5" xlink:type="arc" xbrldt:closed="true" xbrldt:contextElement="segment" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeAxis" xlink:label="loc_us-gaap_SubsequentEventTypeAxis_FE69447AED658B2EF2CD9E0DCF9E7D9E" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_SubsequentEventTable_33B5871803204C960E0A9E0DCF9D9DF5" xlink:to="loc_us-gaap_SubsequentEventTypeAxis_FE69447AED658B2EF2CD9E0DCF9E7D9E" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_5DEA6AA4ACE9396AC9299E0DCF9E5624_default" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_FE69447AED658B2EF2CD9E0DCF9E7D9E" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_5DEA6AA4ACE9396AC9299E0DCF9E5624_default" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventTypeDomain" xlink:label="loc_us-gaap_SubsequentEventTypeDomain_5DEA6AA4ACE9396AC9299E0DCF9E5624" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_SubsequentEventTypeAxis_FE69447AED658B2EF2CD9E0DCF9E7D9E" xlink:to="loc_us-gaap_SubsequentEventTypeDomain_5DEA6AA4ACE9396AC9299E0DCF9E5624" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_SubsequentEventMember" xlink:label="loc_us-gaap_SubsequentEventMember_6F3C2E55D58806883E7F9E0DCF9E7D00" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventTypeDomain_5DEA6AA4ACE9396AC9299E0DCF9E5624" xlink:to="loc_us-gaap_SubsequentEventMember_6F3C2E55D58806883E7F9E0DCF9E7D00" xlink:type="arc" />
    <link:loc xlink:href="http://xbrl.fasb.org/us-gaap/2017/elts/us-gaap-2017-01-31.xsd#us-gaap_StockholdersEquityNoteStockSplitConversionRatio1" xlink:label="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_37A48479FDE0E9E6BD3C9E0DCF9FF28B" xlink:type="locator" />
    <link:definitionArc order="1" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SubsequentEventLineItems_EDA0E953871C6D65EB8D9E0DCF9F9E33" xlink:to="loc_us-gaap_StockholdersEquityNoteStockSplitConversionRatio1_37A48479FDE0E9E6BD3C9E0DCF9FF28B" xlink:type="arc" />
  </link:definitionLink>
</link:linkbase>
