sealisnotcompressed andthelowertrackrollerisstillcapturedbetweenthelowerbearingpadandthe push-offreactionpad.Noticethattogettothefirstrampcontact,theupperrollerhadtohitthepush-off block.Asthemechanism turnspastfirstrampcontact,theflexuresstarttodeflectandrotate,applyinga forcetocompresstheseal.Whenthesealisfullycompressed, thelowertrackrollerisnolongeroverthe push-offreactionpad.Justpastthispointtherampchangesslopetoasmallerrampangle.Intheinitial design,therampinflectionandthefullycompressed sealbothoccurredatthesameposition.Thiswas donetominimizethetorquerequiredtodrivethetrackrollersuptheramps.Whentheflexuresstiffened duringthedesigniterationthatresultedinthekickringandcoverflexure,sealcompression occurred slightlyearlier.Therampswerenotredesigned sinceenoughtorquemarginremainedintheLockRing DriveMechanism. Neartheendoftraveltherampchangestoaflat.Inthelockedpositionat12.5°,the regular flexures havedeflected 0.96mm(0.038in)androtatedthrough 1°tothehorizontal position while the2stiffflexures havedeflected 0.43mm(0.017in)androtated 20alsotohorizontal. Totalpreload on theseparable interface is21,218N(4770Ibf). Duringunlocking, thesameforce/deflection profileisfollowed inreverse. Ifthereisstiction between the coverflangeandtheseal,theuppertrackrollersactonthetwopush-off blocksopposite thehingelineto createasignificant pryingforceateachpush-off block.Theshorting blockstiffens theloadpathsothat theactionofthepush-off forcedoesnotcausethebending beamflexures tobendintheopposite direction, shortening thepush-off stroke. Thepush-off strokewasmeasured duringcharacterization of theEngineering Modelcanister. TheLockRingMechanism wasstopped whentheuppertrackrollers wereatthecenterofthepush-off blocks. Withnosignofstiction present, thegapattheseparable interface between thetwopush-off blockswasthreetimesthesealcrownheight. Thegaptapered offto 1.5timesthesealcrownheightatthetwopointshalfway between theLockRingDriveMechanism and theCoverDriveMechanism. Withstictionpresent, someofthispush-off strokewouldbetakenupby deflection intheintegral coverflexure. IntheLockRingMechanism, therearedesigntradeoffs between therampprofile,thetorquerequired to lockthering,andthelockringflexuredesign. Anadditional tradeoff existsbetween thecapture rangeof thedeviceandthepush-off stroke. Inordertocontact thepush-off blockduringunlocking, theupper trackrollermustalsocontact theblockduringlocking. Thisinitiallyraisesthecoverasmallamount duringlocking andreduces thecapture range. TheLockRingDriveMechanism (Figures 8a,8b,and9)provides torquetolockandunlocktheLockRing andtooperate theArrayLatchMechanism. Themechanism consists ofadual-wound, electronicallycommutated gearmotor withredundant Halleffectrotorposition sensors anddriveelectronics. The gearmotor drivesintoapinionandsectorgeartrain mounted ontheLockRing.Thegearratioofthe pinionandsectoris22.3:1. Thegearing inthemotorisafourstageplanetary withanoverallratioof 2160:1. Radialloadsfromthegearmesharereacted intothetrackrollerandbearing assembly ofthe mechanism ratherthandirectly intotheLockRingtominimize LockRingdeflection andmaintain the correctgearmesh.Themechanism operates bydrivingintohardstopsattheendoftravelineach direction untilatimeout occurs. Microswitches provide confirmation thatthemechanism arrivedatthe hardstop.Themechanism operates ataconstant speedofabout0.0524 rad/s(0.5rpm)duetospeed controlinthedriveelectronics. Traveling between hardstopstakesabout98seconds duringunlocking and100seconds duringlocking. The"NoOpen"functional testisperformed toconfirm themechanism operation without opening the canister cover. Duringthe"NoOpen"functional test,thecoverandbaseareclamped together with external clamps tomaintain thesealandthepush-off blocksareremoved. TheLockRingMechanism canthenbeoperated overitsfullrangetoverifyproperfunction. Testine Figure10showstheresultsofafunctional testoftheLockRingMechanism atroomtemperature during bothlockingandunlocking. Thepredicted locking torqueisalsoshownforcomparison. Thepeak required torqueof16.5N,m(146.4inolbf)occursat6.2°duringlocking. Theshapeoftheactuallocking 201