MicroSatcouldbeaddeddirectlyontoapreviously dockedMicroSatwithouttheneedformultiple interfacelocationsontheClient. Inaparallelprocess,thedesignteamtradedmanydifferentmethodsofjoining,grappling,andaligning. Therewereprimarilyfourdifferentconceptsthatsurfaced.Ideasincluded: •"harpoon"configuration •atelescoping probe •impactdockingwithalargeconicalguide •"claw-type" linkagesinterfacingwithtrefoil Theharpoonconfiguration, inwhichaprobeislaunchedatatarget,latcheson,andisreeledbackinto guidefeaturestocompletethedockingprocess,seemedinherentlyunpredictable andpresented complications concerning thealignmentoffluidandelectricalcouplings.Atelescoping probe,wherea telescoping poleextendstothematingspacecraft, engagesatargetfeature,andretractstojointhetwo, turnedintoacomplicated multi-mechanism apparatusnotwellsuitedforthedirectionandvisiontaking form.Impactdockingwaseliminated asanoptionbecausesoftdockingseemedsaferforthetwo spacecraftandbettersuitedtopreciselyalignfluidandelectricalcouplings.Intheend,theapplication of linkageassemblies interfacingwithatrefoilwasfoundtobethesimplestandmosteffectivemeansto reachout,grasp,pullin,andlatch. Differentoptionswereexploredforprovidingthemotiveforceswithinthemechanism. Nitinol(ashapememoryalloy)wasconsidered. Becausetheprogramwasaresearcheffortandbecausetheapplication ofNitinolwasthefocusoftheinitialdesigneffort,muchtimewasspentunderstanding thismaterial.This materialcangenerateworkthroughaphasechangetransformation thatreturnsthematerialtoan unstrainedstate(about2-4%).Thematerial,whenheated,changeslatticestructureand"remembers" theunstrainedconfiguration, performingworkasitreturns.Theactualstrokeisgenerallyveryshort,and intheend,becauseweweremovingtowardssoftdockingwiththeneedtocreateeffectivelylongstrokes, Nitinolprovedtobeillsuitedfortheapplication. Theuseofwaxandparaffinactuators,acoreSRC technology, wasalsoconsidered. Thistechnology involvesheatingwaxinacontainedspaceandusing theexpansioninvolumeduetoaphasechangefromasolidtoaliquidstatetoproducework(generally intheformofaHighOutputParaffin(HOP)actuator).Hereagain,thistechnology innotwellsuitedfor longstrokeapplications. Theapplication ofagearmotorandleadscrewwasevaluatedaswell.Clearly, highforcesandlongstrokescouldbeachievedusingthistechnology. Design Objectives Thenextphaseinthedevelopment process became oneofdefining aconcrete setofdesignobjectives. Current technology hadbeenexplored andpossible mission scenarios hadbeendefined. Therewasnow something tangible towhichasetofdocking system requirements couldbeapplied. Fundamentally, the design objective wastoprovide asimple means ofdocking, aligning, andlatching twospacecraft autonomously 1.Through aseriesofbrainstorming sessions, thefollowing setofprimary objectives was defined. •provide interface spaceforcouplings •keepitsimple •accommodate auniversal interface •maximize costeffectiveness •accommodate designscalability 1Assumptions weremadethatagivencontrolsystem existed whichwassophisticated enough toposition twospacecraft withinsomeknownrange. Thedesigngoalbecame oneofcompleting thedocking task only.Therewasnofocusorintention ondeveloping orincorporation anysensors orguidance technology intothedesign. NASA/CP--2002-211506 267