,_tru(;:tural inteqrity Thequestion ofwhatisthedesignloadisacriticaloneforTWA,too.Thestructural integrity oftheMarman clampisalwaysamajorconcern. TheMarman clampstructural analysis hastwodifficulties: knowledge of loadcasesandtheanalysis itself.Aninstrument development teamisgiventhefollowing mechanical loads quasi-static limitloade.g.intheformofmass-acceleration-curve inaxialandlateraldirections sinusoidal vibration testloadsalongX-,Y,andZ-axis random vibration loadsalongX-,Y-andZ-axis shockloadsalongX-,Y-andZ-axis(bothdirections) acoustic load Generally, mechanisms arecompact andstiffentities thatarenotacoustically excited. Insomecases,the acoustics onthepanelsthemechanisms support causelargeloadsonthemechanisms. Acoustic and shockloadshavebeenhandled byassessment anddesignsofar.Sinusoidal vibration testisthestrength testforinstruments inplaceofastaticloadtest.Itandrandom vibration canbehandled wellbymodem FEM-software packages suchasI-DEAS. InRussian programs, thetestloadsaretheworstloadcases andthisisagoodapproach: theseloading casesareverified bytesting. InESAandNASAprograms, the worstloadcasemustbefoundfromthefirstthreecases.Thedirection andcombination ofthequasi-static limitloadcomponents hasneverbeendefined wellandactually almostanycombination willdo.Thiscase isnotverified bytesting, fortunately. Thevalueofsuchstaticstressanalysis isdoubtful. Thestructural analysis oftheMarman clampisdifficult usingFEMbecause therearecontacts thatarehard tomodelandcontact elements prohibit eigenfrequency analysis. Marman clamps havebeenstudiedin recentyearsandsomestudies [17]indicate thattheMarman clampsoflaunchvehicles havebeengrossly overdesigned fordecades. InESA,Saabhasstudied [16]Marman clampstructural analysis indetail.At VTTAutomation, muchoftheanalysis hasbeendoneusingMathCAD andanalytic methods. Theissueof tension decrease caused bycreepduringthestorage beforehasarisenintheTWINS project. Creepis hardtoevaluate byanalysis because ofthelackofmaterial properties. Testing canbedone.Onesolution istensioning theMarman clampbeforethelaunch. AHOPactuator opensthelaunchlatch.Theentireactuator withthelatching mechanism isenclosed insideacagethatsupports themulti-layer insulation (MLI).ML1gage,newconnector locations and external limitsbythespacecraft causemerechange fromtwotothreespacecraft connectors intoseveral designchanges. Theconflictcouldbefoundeasilywitha3D-modeler butatthebeginning oftheproject, ACT'sold2Ddrawings wereusedasthebaseline. EMCandmassgrowth InthecaseofTWINS, thespacecraft tolerates highermagnetic emissions thanCassini did.100grams wasintended tobedecreased byremoving thep-metal shieldaroundthemotor.ForTWA,potentially magnetic stainless steelbearings byKaydon wereordered. ThentheTWINS teamrealized thattheir detectors dohavemagnetic fieldrequirements. Fortunately therequirement waslooseenough. Stainless steelbearings areacceptable andmaybethewmetal canberemoved. TWA'sEMCemission limitismuchlowerthanforACT.Betterelectrical coupling between thestaticand therotating partoftheactuator isrequired tobringtheactuator toasinglepotential. Printedcircuitboards mustbecovered withmetalshields. Thereisenough spaceforallthisbuttheundesirable massgrowthis evidentevenforasecond-generation unit. Motioncontrolandlubrication Thepointing oftheTWAismoreaccurate thanthatofACT.Thisrequired amoreaccurate potentiometer. Thistime,themanufacturer, Betatronics [15],wasfoundquickly. TosomeextentWWWhasbecome a sourceofinformation butmainlyfasterprocurement iscaused byexperience inthespacecraft mechanisms. 261