matched,butthecountersunk screwsdidnotseatproperly.ThiscanbeseeninFigure5.Thisrequired reworktoensuretheheadswerebelowflushontheinsideofthecanister. Tosummarize this,accommodating thelargerpayloadandlongerlength,whichwouldseemtobemajor impactshadminimalimpact.Meanwhile thesmalldetailscreatedsomeunforeseen timeandeffort. Changesareaninevitablepartofdesignandshouldbeexpected.Thequestionis:Howcouldwehave preventedtheproblemsthatcameaboutasaresult? Onthetighttoleranceissue,itisaxiomaticthattighttolerancescostmoneyandtime.TheMarmanclamp bandangleprofiletolerancewasstated;however,we(andourmachineshopvendor)didn'tfully understand theimpactofthistolerance.Thelessonfromthisis,becarefulwithtight.angulartolerances. Whenestimatingtheimpactofdesignchanges,ithelpstoconsidertheimpactofverifyingadditional interfacedimensions andtominimizethemasmuchaspossible. Whenworkingcustomerinterfacesoncircularmountings, adecisionhastobemadeatthemanufacturing levelonhowthepartscanbestbemade.Becauseoftheprocess,itwaseasiertoputtheholesinthe canisterintheflatpatternandthenrollthecanistertosize.Thismakestheholesradial.Thebrackets weremoreeasilymadewithholesparalleltotheradialdirection.Inthiscase,theeasiestwaytomakethe designworkistoputradialholesinthebracketsratherthaninthecanister,butthiscostthecustomer providingthepartsmore.Ifoverallcostisthefinalarbiter,thebracketsshouldbemadewiththeholesin theradialdirection.Havingmanufacturing lookatthechangespriortotheiracceptance mighthave spottedthebestwaytogo. Material Problems Duringtheprogram, weusedourheritage asmuchaspossible. Theoriginal breadboard designuseda Teflon-impregnated nickelcoating onallrubbing surfaces onthetubes.Wedecided earlyintheprogram tostickwiththisproven configuration toreduce risk.However, thisresulted inathermal problem that became amaterial problem. Ourthermal analysis showed thecomponent temperatures insidethecanister wouldexceed +60°Cdue totheabsorbtance/emittance (o_/_=0.82/0.85) properties ofthenickelcoating ontheinsideandoutside ofthetubes.Thiswouldcausethemotortoexceed its60°Cmaximum operating temperature range.To reduce temperatures, weanodized theoutside ofthetubesandchanged theabsorbtance/emittance properties toc_/s=0.40/0.82. Thisreduced themotortemperature to55°C.Inkeeping withourheritage, wekepttheinsidesurface ofnickel,whichcreated aprocessing problem. Weaskedourvendors ifthey haddoneanypartsthatwerebothanodized andnickel-plated andtheyhadnot.Wealsoaskedwhat orderofprocessing theywouldprefer.Eachvendor wanted theircoating putonfirst,whichwasnohelp. Ourmaterials research indicated thattheanodize shouldgoonfirstbecause theanodize wouldnotbe damaged bythechemicals usedtoprepare forthenickelplating. Additionally, themasking forthe anodize wasmorelikelytowithstand theplatingchemicals, whilethemasking forthenickelwouldnot survive intheacidbathfortheanodize. Weproceeded withthisorderofoperation anditworked fineforallofthepartsexceptone.Thecanister shell,whichwas7075aluminum alloy,cameinwithsmallpitsinthestructure thatcaused ustorejectit. Review ofthescrapped canister material traceshowed thatitwasmarginal initsresponse toheat treating asmeasured byconductivity. Thespecification allowsreheat-treating tomeetspecification and thiswasdone.Afterheattreating, machining, anodizing, andplating, thepitswerefoundbutonlywhere theoriginal millmarkings werelocated. Wesuspected thatthematerial itselfhadaproblem, sowesent outcoupons ofnew7075-canister material andhadonesetnickel-plated ononesidefirst,thenanodized second. Theothersethadtheanodize first.Results forthesamples showed nopitting,andthatthebest process orderwasanodize first,nickelplatenext.Ourconclusion wasthatthenewcanister material wouldbeacceptable basedonthesetestssoweproceeded withplatingandthenewcanister turnedout NASA/CP--2002-211506 157