Design ofaRobotic WristandTool-Exchange Mechanism forSatellite Servicing Russell D.Howard* Abstract Thispaperdescribes someofthetechnical challenges encountered indesigning theRanger telerobot wristandtool-exchange mechanism, andthedesign approaches usedtoovercome them.Awrist geometry withfourintersecting andindependent, butnotorthogonal, axeswasdeveloped. Itisshownto haveconsiderable advantages overprevious designs, particularly inextending thewrist's angular workspace andreducing thetool-to-wrist centerdistance. Also,acompact five-state mechanism fortool exchange isdescribed. Thisdeviceensures securetooltransfer between themanipulator andastorage facility,whiletolerating significant initialmisalignment. Introduction TheSpaceSystems Laboratory (SSL)attheUniversity ofMaryland haslongbeeninterested inthe operational aspects ofperforming workinspace,suchassatellite assembly andservicing. Initialstudies indicated thattheproductivity ofahuman duringextravehicular activity (EVA)couldbeconsiderably enhanced usingmechanical devices toposition thehuman, carrytoolsandreplacement parts,provide auxiliary camera views,etc.TheSSLhasbuiltavarietyofsuchdevices andevaluated theminsimulated spaceoperations, primarily usingtheneutral-buoyancy environment. Further benefits couldaccruewithamulti-degree-of-freedom remotely-controlled manipulator system, i.e. atelerobot. Suchasystem hasthepotential ofreducing thenumber ofhumans required onsite,and ultimately operating byitselfatsitesinaccessible tohuman crewmembers. Stepsinthatdirection have already beentakenbyNASAwiththeShuttle andStation Remote Manipulator Systems (RMS)andthe Special Purpose Dexterous Manipulator (SPDM). However, thesesystems haveveryspecific functions anddonotoverlap thecapabilities ofahuman inEVAtoagreatextent. Asaresult,in1992theSSLbegandevelopment ofageneral-purpose manipulator system calledRanger. Itscandidate tasksetincludes servicing operations fromtheHubble Space Telescope andthe International Space Station, worksite preparation tasksforhuman EVA,aswellasmoregeneric manipulation tasks.TheRanger program wasplanned toresultinflight-qualified hardware capable of performing serious workinspace, ratherthanaseriesofbenchtop experiments orlaboratory demonstrations. Thefirstfullsetofhardware hasnowbeenbuiltandisundertest.Thepurpose ofthis paperistodescribe someofthemorechallenging design goalsforRanger andhowtheyhavebeen accomplished. Ranger Desi.qn Obiectives TheRanger designphilosophy isbasedonlessons learned fromavariety ofsources: videorecords of RMSoperations, theGerman ROTEX Spacelab experiment andtheJapanese satellite ETS-7, aswellas SSLpersonnel's experience usingtelerobotic testbeds atNASAMarshall SpaceFlightCenter, Johnson SpaceCenter, theJetPropulsion Laboratory, theMassachusetts Institute ofTechnology's Man-Machine Laboratory, andFlightTelerobotic Servicer simulators atGoddard SpaceFlightCenter. TheSSLhasalso performed several paperstudies1'2investigating theutilityofvarious levelsofsatellite servicing capability. Theresulting ideashavebeentestedandrefined withcomputer simulations andaseriesoftelerobotic neutral-buoyancy vehicles 3including theBeam-Assembly Teleoperator (operational 1984-1997), the Multi-mode Proximity Operations Device (operational 1986-1999), theSecondary Camera Platform (operational 1992-present), thefirst-generation Ranger Neutral-Buoyancy Vehicle (RNBV-1, operational *University ofMaryland, College Park,MD Proceedings ofthe3_hAerospace Mechanisms Symposium, GlennResearch Center,May15-17,2002 NASA/CP--2002-211506 117