Theflightpanelreceptacles (Figure 6)aremachined fromA286stainless. Thepinandreceptacle materials combination wasselected tominimize thepossibility ofgallingasthepinwasguidedintothe receptacle. Theinternal geometry ofthereceptacle consists ofanouter45-degree half-angle coneand aninner10-degree half-angle conewithaflatbottom. Theinnerconematches thepin,thelargerangle outerconeaccommodates greater initialmisalignment withlesstotalinsertion length. Theuseoftwo different flat-bottomed receptacles andtheflatendedpinsprevents binding orlockingofthepinsand accommodates thermal distortions andmanufacturing tolerances. Plate-to-plate alignment wasmost criticalfortheelectrical connectors. Toreducethealignment errorattheelectrical connectors, theinner coneofthereceptacle nearest theconnectors wastoleranced tobecome tightsimultaneously withtheflat ofthepinbottoming inthereceptacle. Theinnerconeoftheotherthreereceptacles wastoleranced to allowaslightradialclearance withthepinsbottomed inthereceptacles (Figure 8).Thissmallradialfloat (0.127mm)accommodates theexpected panel-to-panel variations, yetallowsonlyaslightrelative rotation between thepanels. Thegeometry ofthealignment system locates thecriticalelectrical connectors within0.04mmwhentheplatesareinthermal equilibrium. Retract LatchMechanism Theumbilical retractmechanism supports thegroundumbilical panel,compliance mechanism, translating frame,hoses,andcablesintheextended position. Following liftoff,thelatchmechanism isreleased, allowing thetranslating frameandtherestoftheumbilical tofree-fall intotheumbilical tunnel. Thelatch mechanism mustbefastactingandreliableforbothremaining latched andunlatching oncommand. Retract LatchMechanism Requirements Someofthesignificant designrequirements forthepanelalignment mechanism were: •Provide loadcapacity whenlatched of18kN •Unlatch inlessthan250msfromvehiclefirstmotion •Tolerate asinglefailureforlatchandunlatch •Latchautomatically onframeextension •Usestoredenergyforactuation Retract LatchMechanism Description Theretractlatchmechanism usesfourspring-extend, pneumatic retractlatchassemblies arranged in matingpairs.Onehalfofeachpairismounted tothetranslating frame.Theotherhalfofeachpairis mounted totheumbilical tunnel(Figure9).Eachlatchassembly isactuated byadedicated controlvalve located ononeoftheaxialstrutsofthecompliance mechanism. Thelatchvalvesaresupplied froma gaseous nitrogen accumulator charged to17MPaoThelatcharrangement shownissinglefailuretolerant forsupporting theloadandalsoforensuring release. Sinceanylatchpairwillsupport theentireload,the inadvertent release ofanysinglelatchwillnotallowthetranslating frametodrop.Similarly, onlyone latchofeachpairmustrelease inordertoallowthetranslating frametodrop.The250msmaximum operating timeissomewhat misleading. Duetothefactthatthevehicle mayliftofffromanypointovera 8cmrange,thelatchvalvemaynotbeactuated untilthevehiclehasrisenover8cm.Thisresultsinan available operating timeofonly150ms.Analysis showed that,withproperpneumatic flowcapacities, the 150mstargetwasachievable. Thelatchassembly (Figure 10)iscomprised ofastructural steelhousing, steellatch,bronzepivot bearings, andaspecially designed pneumatic cylinder. Thelatchprofileiscircular toprevent liftingofthe assembly duringunlatching. Thespringreturnpneumatic cylinder (5cmbore,8cmstroke)wasdesigned withoversize portsforhighspeedoperation. Inordertoobtainthedesired latchspeed(30msstroke time),thecylinder working pressure wasapproximately threetimesthepressure required tooperated the latchstatically. This,combined withthefactthatloadiszeroattheendofstrokeandsomelatches operate withnoresisting force,created theneedforsignificant cushioning inthecylinder. Both pneumatic andelastomeric cushioning wereincluded inthedesign. Spaceconstraints dictated thatfor eachlatchpair,onecylinder wouldextendtooperate, theotherwouldretract. Otherwise, allfourlatches areidentical. 351