showstheP6sideoftheinterfaceplane.TheP6nadirfacecontainsthecapturebar,fourcoarse alignmentcones,andfourfinealignmentnutassemblies. Operatin.q Phases Thetrussberthing andattachment hasfourdistinct operating phases: PhaseI-SRMS positioning, Phase II-interface alignment, PhaseIll-boltdown,andPhaseIV-demating. PhaseIconsists ofmanipulating the P6intoposition neartheZ1,usingtheSRMS. TheP6ispositioned usingtheSpaceVisionSystem sothat allfourP6coarse alignment coneshavetheircylindrical tipsatorbelowtheplaneoftheZlcoarse alignment bushing faces.Meeting thatReadytoLatch(RTL)criteria ensures thattheP6segment's capture barisplaced withinthecapture envelope oftheZlcapture latch.TheEVAastronauts visually verifythatthereadytolatchcondition hasbeenachieved, completing PhaseIoperations. InPhaseII,astronauts usetheelectricwrench toclosetheZ1capture latch.Asthelatchclawscloseupon theP6capture bartheZ1andP6segments arepulledtogether, thefinealignment features engage, and theP6moveslaterally withrespect totheZ1.TheSRMSisplaced initsTestmodeduringPhaseIIto reduce resistance tothefinealignment. SRMSTestmodeisa"limped" modeinwhichthejointservos havenocontrolauthority andtheSRMSjointsarerelatively compliant toendeffector motion. TheZ1fine alignment/bolt mechanism isshowninFigure6.TheP6longspacernutinstallation isshowninFigure7. Whenthefinealignment cones(shearcylinders) ontheZ1sidefullyseatintheirreceptacles ontheP6, thecapture barisapproximately 6mmfromfullyseated inthecapture latch.Continuing toclosethe capture latchdeflects thecapture bar'sbackup structure, whichproduces asmallpreload between theZ1 andP6structures. Tocomplete PhaseIll,theEVAastronauts firstverifythefinealignment features arefullyseated by checking thegapbetween theP6andZ1housings, usingaconvenient toolofaknownwidth.Next,the crewtightens theprimary structural attachboltstofastenthetrusssegments toeachotherinthe sequence notedinFigure5.Theresulting configuration isshowninFigure8.Theboltdesignincorporates a"self-feeding feature" whichprovides asmallaxialforcetoinitiateboltthreadengagement sothatthe crewmember doesnothavetopushontheendoftheboltduringtightening. Duringtightening, thecrew checks thattheboltisturning, advancing, andtherunning torqueislow.Theboltpreload iscontrolled by torquealone.Primary boltinstallation torqueisreacted bytwopinsintheZ1shearcylinder engaging matching slotsintheP6primary balls.Aftertheboltsarefullytightened, thepreload applied bythecapture latchisreleased byEVAactuation, theSRMSungrapples theP6,andtheattachment process (Phase III) iscomplete. LaterintheISSassembly sequence, theP6isremoved fromtheZ1andmoved toa permanent location ontheoutboard truss,atP5.ThePhase IVtasksassociated withthedemating operation arethereverse ofPhases Ithrough III. Where possible, thethreephases associated withtrussberthing andmating areseparate andhave distinct, identifiable beginning andending points. Inaddition, confidence forproceeding withthenext phasecanbegained byestablishing specific verification criteria. Forexample, theinterface alignment phaseisverified complete priortoinitiating boltoperations, bychecking thatthefinealignment features haveaccomplished thelateralpositioning, andthatthecapture latchhasaccomplished theaxial positioning. Thepractical meansofdetermining thatthealignment hasbeenachieved towithinthedesign limitsofthesystem isbyhavingtheEVAcrewchecktheZItoP6housing distance. Thegapcheck confirms thatthelateraloffsetiswithinthecapability oftheboltthreads toengage thenut,evenwiththe nutrotated withinitsspherical bearing. Capture LatchDescription TheCapture LatchAssembly, mounted ontheZ1truss,consists oftwoopposing clawsconnected toa seriesoflinkages, adrivescrew,andageared drivetrain(Figure 9).Theinputshafttothedrivetrain, whendrivenataconstant 15RPM,willcausetheclawtorotatefromfullyopentofullyclosed in approximately 6minutes 45seconds, although itmaybedrivenfasterorslower. Assuming thecapture bar,asolidsteelcylindrical shaftmounted ontheP6truss,iswithinthesweepareaoftheclaws,theclaws willthenpullthebar,andtheattached P6truss,towards theZ1truss,forcingthetwointerfaces tocomply. ForuseontheZ1,theCLA'sinputisextended byatubetotheouteredgeofthetrusswherethe astronaut hasgoodaccess. 2OO