Thedesignhadtohaveprovisionsandspaceforfluidandelectricalcouplings.Thiswasthegoalfromthe beginningandcontinuedasaprimedriverthroughout. Asimpledesignwouldusealimitednumberofsub-mechanisms thatincorporate efficientmotiveforces andminimizethenumberandcomplexity ofparts.Throughout thetradesandevaluationofdifferent designconcepts,ahighlyscrutinized areawasthequantityofmechanical systemsrequiredtoreachthe objective.Seenthroughearliertrades,optionsarosewhichrequiredmechanisms toreachoutandgrab (i.e.grapple),mechanisms tolatchandrigidize,andmechanisms tocompletethematingoffluidand electricalcouplings.Nitinolandwaxactuatorscouldbeusedalongwithstoredspringenergytocomplete theseseparatefunctions.However,theutilizationofagearmotorandleadscrewwaspreferredsimply becauseasinglemotiveforcecouldperformallthesetasksassociated withsoftdocking.Design conceptsincorporating fewercomplexpartsalsogreatlyinfluencedthedesigndirection.Aclearmethod tominimizethecomplexity ofthesystemwastodevelopacompletely passiveinterfacecomponent (i.e. oneabsentofdrivenmechanisms orpowerrequirements). Inadditiontosimplicity,developing adockingsystemwithanindustrystandardinmindseemedprudent. Adockingsystemshouldbedesignedinawaythatspacecraftmanufacturers couldintegrateacommon interfaceandbeassuredthat,lateron,theinterfacewouldinteractwithastandardservicingspacecraft. It wasclearthataverysimplepassiveinterface,designedtomountasastandardinterfaceonall spacecraft, mustbedevelopedtoworkwithamorecomplexdockingmechanism usedinamorelimited senseontheservicingspacecraftonly. Bystrivingforsimplicityindesignalowcostsolutioncouldbeachieved.TheactivesideoftheMDSwas complexandwouldthereforebemoreexpensive. However,thelowerquantitiesofthemorecomplexand expensivemechanism interfacingwithhigherquantitiesofverysimpleinexpensive passivemechanism provedlesscostlythanthealternative (i.e.tousehigherquantitiesofmorecomplexandexpensive mechanisms ateachinterface). Creatingadesignsimpleenoughtofacilitatescalingbecameanobjectiveastheprojectmatured.There wasalwaysanintentiontoaccommodate differentapplications; thisplayedavitalroleintheeventual configuration. Onebenefitincludestheabilitytodockvarioussizesofspacecraft. Forexample,abaseline preloadincreaseof3times(e.g.,from2224N(5001b)to6672N(15001b))mightresultinanoverall diameterincreaseof2.5times(e.g.,from25.4cm(10in)to61.0cm(24in))allowinglargerspacecraftto dock. Combining primarydesignobjectiveswithconceptsandideasgatheredduringvariousbrainstorming sessions,alistofmorespecificdesignrequirements wascompiled(Referto Table1).Ofparticularnote,alistofguidelinesoutlinedinanAIAApublication2wasincluded. TheScalable Mechanical Docking System Through theprocess ofresearch, mission scenario development, andconcept trades(e.g.,mechanical configurations andmotive forces), adesign direction tookshapethatformed thefoundation ofthe development hardware. Various tradesmadeclearthatthepreferred designanddocking method wasto incorporate asetofthreelinkage assemblies, drivenbyasinglemotor,tointeract withapassive trefoil/interface. Thedesignconcept, intheend,resembled thatdeveloped bytheJapanese (i.e.,JEM). 2"GuidefortheServicable Spacecraft -Grasping/Berthing/Docking Interfaces", American Institute of Aeronautics andAstronautics (AIAA), AIAAG-056-1992, ©1993 NASA/CP--2002-211506 268