Contingency DesiqnandOperational Features InPhaseII,ifthecapture latchfailstoclose,theastronauts havecontingency procedures forrouting special strapsbetween thetrusses andwithawinch,theytemporarily holdtheinterface together during boltengagement 1.Toaccommodate failures inPhase Ill,bolt-down, eachfinealignment device incorporates twocontingency attachment bolt/nut combinations toallowastructural connection tobe madeintheeventtheprimary boltcannotbeengaged (seeFigure8).Ateachcornerofthetruss,the mechanism istwofaulttolerant forachieving structural integrity. Therefore iftheprimary boltcannot be engaged, onecontingency boltcanbeengaged. Ifthatcontingency boltcannot beengaged, thesecond contingency boltcanbeemployed. Specific operational procedures were_orepared through thedevelopment offlowcharts thataddressed potential anomalous on-orbit conditions. Manufacturing tolerances andthermal-structural deflections may createanoffsetbetween thecapture barandthecapture latch(seeFigure10).Theseoffsetsaffectlatch preload andtheabilitytofullyseattheshearcylinders attheshearcarrying corners ofthetruss. Procedures weredevised toloosenthecapture latchifthebar/latch offsetcauses excessive Z1bolttoP6 nutmisalignment, asdetected bythetruss-to-truss gapcheck.Ananalysis wasconducted toderivethe number ofturnsthelatchwouldneedtobeloosened. Contingency boltsandassociated threaded spacers arelaunched withtheZ1intheposition shownin Figure6.EVAastronauts extendthespacersleeve. Thespacerservestomaintain thegapbetween the Z1finealignment housing andtheP6cornerfittingsothatnobending moments arecreated duetothe distance between thefinealignment shearcylinder's centerline andthecontingency bolt'scenterline. A special locktoolisinstalled overthespacer sleevetokeepitfromturning duringcontingency bolt operations (seeFigure11).Thetoolincorporates anadditional feature foruseincontingency operations tomeasure thegapbetween Z1andP6housings3. Ifneeded, thetool'stapered protrusion isplaced between thehousings untiltheedgescontact thehousings. Thehousing gapisindicated bygraduated linesontheprotrusion, whicharevisibletothecrew. Allcontingency nutsinP6finealignment deviceslideinY-Zplane.Eveniftheprimary boltfailstoengage, shearistransferred through theshearcylinders onprimary boltatthetwotrusscorners thatareintended toreactshear.Operational procedures ensure theshearcylinder isseatedeveniftheprimary boltisnot completely engaged. Contingency boltinstallation torqueisreacted byalocking plateontheP6assembly (seeFigure12).After contingency bolttorqueing, thisplateisremoved byEVAandstowed forfutureuse.Aprybarcanbeused toassistinplateremoval whilethecontingency ballflatspressagainst theplate'sslotted hole.Plate removal allowsthecontingency ball/nut racestoslideandrotateasrequired toaccommodate thermalstructural deflections. Ifthecapture latchcannot bereleased nominally, therearebackup means torelease thepreload by turning theP6capture barinitseccentric bushings, andreleasing theZ1capture latchclawsviaEVA handles ontheZ1zenithbulkhead 2. Fordemating (Phase IV),thedeviceincludes arelease mechanism, anEVAoperated lockpin,toallow disconnect oftheP6fromtheZ1shouldtheprimary EVAboltbecome stuckintheP6sleeved nut(see Figure12)duringengagement. Ifthenutgetsstuck,contingency toolsandmeans existtoreplace thenut (threaded sleeve) intheP6finealignment assembly, thereby restoring theoriginal fault-tolerance ofthe jointforconnection ofP6toP5.Theself-feeding nutintheZ1boltassembly ismadeofplasticwhichwill shearoffasthebolt/nut together areunscrewed, ifthebolthasstucktothenutatasignificant engagement depth.Thisfeature isrequired because thereisasmalldifference inthreadpitchbetween theouterandinnerdiameters oftheP6sleeve/nut. Thermal-Structural Analysis Theaccommodation ofstructural deflections caused bythetemperature gradients wasoneofthemost important considerations indesigning thetrussattachment system. Estimates ofthetemperature distributions weremadeusingISSthermal models ofboththepre-mate andpost-mated conditions. Transient thermal analysis wasusedtodetermine trusstemperatures atthepointintimewhenthemating wasexpected tooccur.Numerous flightattitudes, sunangles, hardware configurations, shadowing, and 201