JointPreload Considerations Theprimary andcontingency boltsmustbetightened toasufficiently hightorquetocreateapreload that prevents jointseparation undertheinfluence ofexternal loads.Themaximum torqueislimitedbystrength, fracture andfatigue considerations. Withupperandlowerlimitsdefined, arangeofpermitted torque values istherefore determined. Typically, another factormustbetakenintoaccount- thechange in preload associated withtightening theboltatthevarious predicted on-orbit temperatures, duetothe difference inthermal expansion coefficients between theboltandclamped materials. Inthecaseofthe subject attach system, however, thebolt,shearcylinder, retaining nut,andthreaded sleeve areall stainless steelalloyswithsimilarcoefficients ofthermal expansion. Variations inbolt-nut interface friction coefficients areexamined inthejointanalysis thatplaceadditional constraints onthebolttorqueallowable range.Development testswereconducted tocharacterize thefriction coefficients associated withthe specific materials, sizes,surface finishes, andlubricants ofthetrussattachsystem jointss.Thesetests wereconducted inair,andatvacuum, overtheexpected temperature range.Theattachbolts,races,balls andnutsaredryfilmlubricated withMolybdenum Disulfide. Theprimary boltsizingcalculations included misalignment loadsassociated withclosing amaximum axial gapthatmayexistatthetimeofbolt-up, duetotruss-to-truss interface out-of-plane manufacturing tolerances andthermal-structural deflections. Thecontingency boltsizingdidnotinclude thismisalignment loadbecause thecontingency spacer sleeve bridges, butdoesnotclose,theaxialgap.On-orbit mechanical loadsarealsopartofthejointdesignloads. Afterthepreload rangewascomputed, thetorque rangewasdetermined andawrench withadequate torqueaccuracy wasselected _.Inthecaseofthesubject trussattachment system, thefinaltightening of theboltswasaccomplished usingamanual torquewrench thathadanaccuracy of+/-10% inthe expected operating andtorqueranges. Design Tolerance Studies Alargenumber oftolerance analyses wereperformed toensure thattheselected designdimensions of thetrussattachment system features provide therequired performance inthedifferent operating phasesz. Thissection describes theevaluations oftrussin-plane differential displacement, out-of-plane relative displacement, andrelative rotations duetowarpage. Inaddition, studies oftheclearances ofthemoving elements areaddressed. During andaftermating, temperature gradients existwithintheP6andZ1 trusses. Suchgradients causethestructure todeflectfromitsnominal shape.Thetolerance assessment included thermal conditions thatexistduringpre-mate andpost-mate configurations. In-Plane Differential Displacements Analysis wasperformed topredict themaximum thermal-structural displacements inthemating plane, acrosstheZl-P6interface. Relative displacements werepredicted between eachofthefourcornerfine alignment features, between eachofthefourcoarsealignment features, andbetween thecoarseandfine alignment features. Acheckwasmadetoensure radialclearance existsbetween thecoarsealignment P6cone'scylindrical bodyandZ1coarsealignment bushing insidesurface whendisplacements areattheirextremes. The coarsealignment features musthaveclearance post-mating, sothatshearloadsareonlytransmitted at thefinealignment connections. Theanalysis wasrepeated forbothnominal andworstcasedetailpart dimensions, andoverallpositional tolerances. Clearances forpre-mate andpost-mate thermal conditions wereexamined. Theclearance between theP6finealignment primary ball/race andtheP6comerfittingboreforeachof thefourcorners, onetoanother, wasanalyzed aswell.Raceclearances mustexist,post-mating toensure thatshearloadsarereacted bytheintended statically determinate system. Acalculation wasmadetodetermine theradialclearance between thefinealignment Z1shearcylinder andtheP6receptacle (nut)whenthesetwoitemsfirstbegintoengage (bycapture latchclosure). The calculation wasrepeated withtheitemsdisplaced bythermal-structural gradients andmanufacturing tolerances. Adetailed layoutrevealed thattheshearcylinder wouldentertheballproperly. 203