TheChallenge TheprojectbeganwithaSmallBusiness Innovative Research (SBIR)grantfromtheAirForceResearch Laboratory (AFRL). SRCsuccessfully proposed adesigntodocktwosmallspacecraft usingNitinolshape memory alloywithinthecoupling members. AFRLhadaproject calledXSS-11 thatincluded an experimental mission wheretwocoupled spacecraft werelaunched intoorbit.Uponreaching stableorbit, theexperiment wastoseparate andre-jointhestructures. Afterthespacecraft became re-latched in place,atransfer ofwaterwastooccur,andthusdemonstrate thetechnology forfuturedevelopment. Fromearlyoninthedesign effort,thegroupwasworking withonlyageneral concept inmind.AFRL awarded thegranttopromote development oftechnology applicable tofuturedocking needs. They provided bounding conditions totheproblem thatincluded anestimated spacecraft sizeandmass(a cylinder, 50cmODx130cmL,50kg)andarequirement todocktwospacecraft andtransfer fluidand/or electrical databetween them.Without aspecific andconcrete design goal,thetaskofcreating a meaningful mechanism necessitated stepping backandlooking atthedesignfromanentirely newpoint ofview.Adefinition ofthevarious needsthatmightarisewhenservicing obsolete orexhausted spacecraft hadtobeformulated. Thechallenge became oneofestablishing requirements tomeetthe needsofaconcept ratherthandesigning tosolveproblems basedonaclearly defined setof requirements. Aresearch effortwasundertaken toevaluate existing technologies. Theresultwasverydiscouraging. Mostavailable technology relatedtoextra-vehicular activity (EVA)interfaces, robotic boomend-effector configurations, orimpactdocking mechanisms. EVAtechnology usedonorbitalreplacement unit(ORU) mounting interfaces yielded someideasaboutalignment andlatching. Thistechnology wasbyitsnature intended formanned intervention. Grappling technology developed asroboticend-effectors usedonthe shuttle (e.g.Remote Manipulator System (RMS)), presented otherideasonmechanical interface configurations. TheRMSboomend-effector wasdesigned tograpple payloads andallowastronauts to moveandplaceobjects. Thismechanism wasverycomplex andlargeandittended tofalloutside the emerging designgoals.Othertechnologies, however, werespecifically relatedtospacecraft-to-spacecraft docking. Examples ofbothimpactdocking and"soft"docking werefound.Mechanisms suchasApolloSoyuzUniversal Docking Interface, ApolloProbeandDrogue Docking Assembly, andGemini-Agena Docking System werereviewed. Thesesystems wereprimarily intended forlargespacecraft andimpact docking applications. Theywerenotwellsuitedforthemoreprecise requirements ofautonomously soft docking andaligning fluid/electrical couplings. Afewsoft-docking interface examples werefoundwhere linkage assemblies provide themeans ofcapture. Oneexample demonstrated aseriesoflinkage/latch assemblies around alargeinterface perimeter. These assemblies operated independently tolatch together matingspacecraft. Another, theJapanese Experiment Module (JEM),utilized linkage assemblies toengage atrefoilinterface onthematingspacecraft. Therewasalsoaclearneedtodefinetheeventual useandapplication ofthisintended mechanical docking system. Further research didnotyieldanydefinitive mission scenarios. However, itdidpresent thedesignteamwithgeneral ideasabouthowadocking system mightbeapplied. Itwasbelieved thatby defining thesepossible mission scenarios, adocking system couldbedesigned andtailored specifically forthatmission/use. Twomission scenarios wereconceived. •Client(spacecraft inorbitneeding service) /MicroSat (spacecraft servicing theClient)-AMicroSat couldbelaunched onanas-needed basistodirectly service anorbiting client(goodscenario for technology upgrades, refueling, andrepairs) •Various clientsatellites andaMicroSat basestation(bothinorbit)-TheClientcallsontheMicroSat baseasneeded (goodscenario forcommon repairsorrefueling needs). Ineithercase,theMicroSat mightbeusedinanumber ofconfigurations. TheMicroSat maybedesigned tointerface withtheclient,perform atask,anddepart(returntoanorbiting depotortoearth).Itmightalso bedesigned asasingle-use unitthatattaches toandstayswiththeclient.Here,theMicroSats might require anoptiontobestacked. Asafuelcellorcontrol module becomes outdated, anadditional NASA/CP--2002-211506 266