1995-present), andthesecond-generation Ranger Neutral-Buoyancy Vehicle (RNBV-2, operational 2002). Theresulting designphilosophy forasatellite servicing telerobot includes thefollowing tenets: •Twohuman-scale dexterous armsmounted onanarrow basewithintersecting workspaces provide acapable platform. Thearmsshould becapable ofworking inconfined areaswiththe sameaccess requirements imposed forhumanEVAservicing. •Workisdonewithtools.Arigid,repeatable toolgripisessential. Asecuremeansofstowing and retrieving toolsfromastorage facilityisnecessary. •Multiple camera viewsareessential. •Activecompliance isdesirable toavoidinadvertent damage totheworksite, particularly when thereissignificant timedelayinthecontrolloopbetween theworksite andthehumanoperator. A localactivecompliance controller canreactto(andlimit)contact forcesmuchquicker thanthe remoteoperator. •Simplekinematics areimportant. Afrustrating feature commonly encountered usingteleoperated manipulators isfrequent, unexpected violation ofsingularity constraints orjointworkspace boundaries, resulting inuncommanded motion bythemanipulator orarefusal tomove.Simple robotkinematics withfew(orno)offsetsbetween actuation axescanhelp,alongwithkinematic redundancy andatransparent scheme ofmanaging it. •Packaging requires carefulattention. Control electronics shouldbeembedded inthemanipulator wherepossible tominimize wiringlength,protectit,reducevolume, andrenderthearmsmodular, self-contained, andpotentially reconfigurable. Ofcourseatelerobot shouldalsobeprecise, reliable andcapable offunctioning inthespaceenvironment aswellasneutral-buoyancy simulation, i.e.underwater. Thelackofexisting orproposed manipulator systems meeting theseobjectives prompted theSSLtodevelop theRanger design. Specific DesiqnProblems Addressed Someofthemostchallenging designproblems encountered intheRanger program occurred attheends ofthearms:thewristandtool-exchange mechanisms. Thedesireforawristwithsimplekinematics and noobjectionable singularities conflicts withthedesires forlargeangular workspace andcompact packaging. Similarly, itisdifficult toobtainarigid,repeatable, andstrongtoolgripwithasimple, compact mechanism, whileensuring securehandoff to/from atoolstorage device. Initialdesigns wereimplemented inRNBV-1 in19954'5.Overthecourse ofmanysimulated satellite servicing operations, itbecame clearthatthewristandInterchangeable End-Effector Mechanism (IEEM) designshouldbetargets forimprovement inthesecond designiteration. Thisiteration wascompleted in 2001,andresulted inthearmdesign described here.Ithasbeenimplemented onanewneutralbuoyancy vehicle RNBV-2 (operational mid-2002) andaparallel setofspaceflight-qualifiable hardware. Desi.qn Methods Anumber ofcandidate wristgeometries wereevaluated. Eachwasrefined togiveabalance oflarge angular workspace andshorttool-to-wrist centerdistance, takingintoaccount dimensions oftherequired actuators andsensors. Kinematic analyses wereperformed oftheleading candidates toidentify workspace boundaries andsingularities, andtheconsequences oftheseonmanipulator control were investigated. Thefinalwristdesign (Figure 1)incorporates fourindependent degrees offreedom (DOF)plustwotool driveactuators, allofwhoseaxesintersect atasinglepoint.Itcanbedescribed asaskewroll-pitch-yawroll(sRPYR) wrist;"skew"because theanglebetween theinitialrollandpitchaxesis45deginstead of theconventional 90deg.TheinitialrollDOFrotates theentirewristabouttheaxisoftheforearm. The pitchDOFrotatesanarmature oryoke,whichsurrounds aspherical innerwrist.TheyawDOFrotatesthis sphere withintheyoke,andthefinalrollDOFrotatesthemanipulator's outputflangeandanyattached toolsaboutitsaxis,whichextends radially outward fromtheinnersphere. Thetwotooldriveaxesare NASA/CP--2002-211506 118