•¢'_' Z Design andVerification ofSpaceStation EVA-Operated TrussAttachment System Gabriel Katell* Abstract Thispaperdescribes thedesign andverification ofasystem usedtoattachtwosegments ofthe International SpaceStation (ISS).Thissystem wasfirstusedinspacetomatetheP6andZ1trusses together inDecember 2000,through acombination ofrobotic andExtra-Vehicular tasks.Features that provided capture, coarse alignment, andfinealignment during theberthing process aredescribed. Attachment ofthishighvaluehardware wascriticaltotheISS'ssequential assembly, necessitating the inclusion ofbackup design andoperational features. Astronauts checked fortheproperperformance of thealignment andboltingfeatures duringon-orbit operations. Duringberthing, thesystem accommodates truss-to-truss relative displacements thatarecaused bymanufacturing tolerances andon-orbit thermal gradients. Afterboltinstallation, thetrussinterface becomes statically determinate withrespect toin-plane shearloadsandisolates attachboltsfrombending moments. Theapproach usedtoestimate relative displacements andthemeans ofaccommodating themisexplained. Confidence insystem performance wasachieved through acost-effective collection oftestsandanalyses, including thermal, structural, vibration, misalignment, contact dynamics, underwater simulation, andfull-scale functional testing. Design considerations thathavepotential application toothermechanisms include accommodating variations of friction coefficients intheon-orbit joints,wrench torque tolerances, jointpreload, moving element clearances attemperature extremes, andbolt-nut torquereaction. Introduction Theconstruction oftheISSpresents manychallenges duetoitslargesizeandcomplexity. Multiple segments arebrought toorbitviatheSpaceShuttle. Onceon-orbit, thesegments mustbeunberthed from theOrbiter's cargobay,movedtotheISS,thenattached totheISS.Inotherapplications, itmakessense toaccomplish thesetaskssolelyviaautonomous androbotictasks.DuetothecriticalnatureoftheISS power system segments, however, anewattachment system wasdesigned tobeoperated by spacewalking astronauts whocouldquickly reacttoanyproblems encountered duringassembly. The system wasfirstusedtomatetheP6andZ1trusses together. Thispaperdescribes themanydesign considerations associated withthenewattachment system andtheuniqueverification approach usedto gainconfidence insystem performance. TheP6LongSpacer isanintegrated trussstructure thatwillprovide theISSwithpower, usingsolar arraysandbatteries, andcommunications forvoiceandtelemetry. TheP6wascarried intoorbitonSTS97,ISSflight4A,whereitwasattached totherestoftheISSthrough theZ1Truss.TheZ1isan integrated trussstructure thatprovides amating location fortheP6LongSpacer, attitude control hardware, andcommunication hardware fortheISS.TheZ1wascarried intoorbitonSTS-92, ISSflight 3A,whereitwasattached toNode1oftheISS.Figure1showstheZ1element initslaunchconfiguration whileFigure2showstheP6element initslaunchconfiguration. Figure3isaphotograph oftheISSatthe conclusion ofSTS-97, showing theP6attached totheZI. Design andOperations Overview Thetrussattachment system isthehardware usedtoalign,mate,andattachtheP6LongSpacer tothe Z1Integrated TrussAssembly. Themating isaccomplished withtheuseoftheShuttle Remote Manipulator System (SRMS) andExtra-Vehicular Activity (EVA).Thesystem, shown inFigures 4and5, consists offoursetsofcoarsealignment cones/receptacles, foursetsoffinealignment coneswithintegral boltmechanisms andnuts,andacapture latch/capture barmechanism topulltheinterfaces together. Figure4showstheZ1sideoftheinterface plane.TheZ1zenithbulkhead supports theCapture Latch Assembly (CLA),fourcoarse alignment receptacles, andfourfinealignment boltmechanisms. Figure6 *TheBoeingCompany, Canoga Park,CA Proceedings ofthe35_hAerospace Mechanisms Symposium, AmesResearch Center,May9-11,2001 199