torquecurvegenerallyfollowsthepredictedlockingtorquecurvebetweenthefirstrollercontactandfully loadedpositions.Thepeakoftheactualcurveislowerthanpredictedbecauseworstcasefriction assumptions wereusedfortheprediction. Theactualcurveismoreroundedbecausetheprediction assumedthatallthetrackrollersreachthepredictedconditionsatexactlythesametime.Thevariation causesanaveragingeffect.Thesamephenomenon isobservedattheendoftravel.Inordertocreate thedesiredclampingforceateachbendingbeamflexureinthelockedposition,theheightoftheflatpart ofeachrampisindividually adjustedtonullifythetolerancestackupaccumulated bythecoverandbase flanges,thesealretainer,andthelowerbearingpad.Thelockingtorquestartstodropoffatabout10°as someofthetrackrollersreachtheflatpartoftherampmuchearlierthantheothersdo.Theunlocking torqueislowerthanthelockingtorqueastheclampingforceontherampstendstohelpduringunlocking. Duringallfunctionaltesting,thehighesttorquerequiredbythemechanism was22.04N,m(195in*lbf) duringcoldoperation. Duringdynotestingofthemotorsthelowestgearmotorstallvalueobservedwas 73.45N_m(650in,lbf)resultinginaminimumtorquesafetyfactorof3.3. CoverDriveMechanism Recluirements TheCoverDriveMechanism provides torquetoopenandclosethecanister cover.AswiththeLockRing Mechanism, theCoverDriveMechanism mustoperate inlgandmustbecapable ofperforming a functional testtoverifytheflightelectrical interfaces andactuator operation without opening thecanister (the"NoOpen"functional test). Description TheCoverDriveMechanism isillustrated inFigures 11a,1lb,and12.Thesamegearrnotor anddrive electronics areusedinboththeLockRingDriveMechanism andtheCoverDriveMechanism butinthis casethegearmotor drivesdirectly atthecoverhingeaxisusingthehexdriveonthegearmotor instead of thepiniongear.Thedrivehubturnsonalightlyloaded, spring-preloaded bearing pair.Thepreload is notsensitive tothermal changes because ofthespringpreload. Thehingeaxisislocated attheseal crownheight(i.e.abovethemetal-to-metal interface between thecanister coverflangeandtheseal retainer mounted onthecanister baseflange). Positioning thehingeaxisatthesealcrownheightinstead ofatthesealretainer surface minimizes thecapture rangeneeded fromtheLockRingMechanism, however italsorequires covertranslation tosealthecanister whenthelockringengages. Relatively stiff coverarmflexures, integrally machined intothecoverarms,permitthiscovertranslation. Thedesignof thecoverarmflexures wasaparticular challenge. Thetorquetubeisneeded tostiffenthetorsional load pathbetween thetwoarmsbecause onlyonearmisdrivenbythegearmotor. However, thetorquetube occupies agreatdealofspaceinthemechanism leaving littleroomforflexures. Inordertofindroomfor theflexures, thecoverarmattachment pointswerechanged fromamorestraightforward location tothe moreunorthodox attachment scheme showninthefigures. Duringnormaloperation ofthismechanism, thegearmotor turnsthedrivehub,whichisattached byfour fasteners tothedrivearm.Themechanism movesuntilthehardstoparmintegral tothedrivehubhits eithertheopenorclosedhardstop.Atimeout turnsoffthegearmotor command andmicroswitches provide confirmation thatthemechanism reached ahardstop.Duringthe"NoOpen"functional test,the fourfasteners thatholdthedrivearmtothedrivehubareremoved. Nowwhenthegearmotor rotatesthe drivehubthrough thehexdrive,themotionoccursattheCoverDrivecoupling interface (Figure 12) instead ofopening andclosingthecanister cover.Thehardstoparmonthedrivehubisabletomove through thefull180°oftravelbetween thetwohardstopssoboththegearmotor andthemicroswitch operation canbeverified without opening thecanister cover.Thematingsurfaces attheCoverDrive coupling interface aretreated toprevent gallingandtoproduce lowfriction. Thefayingsurfaces ofthe 7075-T73 aluminum armarehardanodized andthecorresponding surfaces onthe15-5steeldrivehub arecovered withadryfilmlubricant, Lub-Lok 4306. 202