Design andManufacturing Lessons Learned Intheefforttoconfigure thetapedriveinacosteffective andreliable embodiment, several designand manufacturing lessons werelearned. Mostoftheselessons involved themethods ofmanufacturing a tapeassembly thatwouldpossess thestrength required aswellasterminate easilyoneachpulleywitha simplemethod oflengthandpreload adjustment. Wireropecableswereoriginally baselined duetothestraightforward termination methods, inherent redundancy ofmultiple strands aswellastheneedtowrapontwoorthogonal pulleysurfaces. Ascables arewrapped around theradiusofapulley,thewirestrands tendtobroomandthecableassumes an elliptical shape.Thisactionofrepeatedly re-nesting thestrands thatmakeupthecablewouldresultin cablelengthvariations thatarenotpredictable. Theerrorincreases astheratioofthediameter ofthe cabletopulleyradiusincreases. Slighterrorsinsynchronization asaresultofslightlengthchanges would introduce endofdeployment errorsthatmustbeaccommodated forinthelatching window. Useof latching window budget isunfavorable asadesign baseline andifpossible should besavedfor unanticipated sources oferror.Also,cableshavealowstiffness atlowpreload. Inordertooperate inthe higherstiffness regionofthecables, largershearloadsonthedrumandstrutcleviswouldberequired resulting inhigherfrictional lossesandloweroverallefficiency ofthenode.Giventhesereasons, cables werereplaced withtapes. Drumtapeanchor Clevistape;anchor showing adjustment screwlocation Figure9.Tapeassembly Tapesneedtotwist90°inordertowraponeachpulleysurface. Thewidthofthetapeisontheorderof 10timesthefreelength. Abuckling pattern inthecenterofathintapecanbeobserved whentwisted. Thisintroduces alowstiffness regime duetothelengthdifference between theoutside andcenterofthe tape.Suchtapesmustbepreloaded sufficiently tostrainthecenterofthetapetoeliminate thisbuckling. Finiteelement modeling showsthatstiffness reductions canbeashighas15%whenoperating inthe buckled regime. Cables typically require preloading intheregionof50to60%ofbreaking strength in ordertooperate inalinearstiffness regime. Thefinaltapegeometry avoided thisbuckling modeby optimization ofthewidthandthickness. Stiffness reduction duetotwistofthefinaltapegeometry wason theorderof2%. Duetocertainloading conditions duringthedeployment ofthearraystructure, thetapedesignrequired a material withahighultimate tensilestrength. Elgiloy® waschosen basedonitsstrength andavailability in various thicknesses. Theyieldstrength varieswithtapethickness. Inthethickness selected, theyield stresswasapproximately 2.0GPa.Theratioofpreload toultimate strength fortheassembly is15%and issettoensurepreload ismaintained underworst-case deployment loadsandthermal conditions. Finding arobustmethod fortapetermination proved tobeanenabling technology fortheconstruction of suchasmallmechanism (thedrumdiameter is38mm).Tapetermination usingconventional pinning and clamping required theuseoffasteners thataretoolargetobepractical ortoosmalltobereliable. Several different methods oftapetermination wereinvestigated including brazing andtapeswithintegral ears. Traditional welding techniques werenotinvestigated initiallyduetopotentially largeresidual stressfields intheheataffected zonesandtheeffectonthetemper ofthetapematerial. Abrazing material wasfound thatcouldbeprocessed attemperatures belowtheannealing temperature ofthetapeandthismethod became theleading candidate. Although material mismatch wouldnotpresent aproblem asitwouldwith welding, uncertainties aboutshearstrength consistency, theabilitytoposition thetapeduringthe process, andpossible outgassing remained. NASA/CPw2002-211506 85