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A solar' array cfriw (SAD) was cksigneci for opc)ration cm ttw 1 C)P[ X/PC)SE lDON spacmmf[ tlIat was Iaunchcj irl Au!gust c)f 1 W?. 1 tic Cxpcriorm gained in selecting, spc!cifying, testing to failure, ar]ci rcdc:signing its fmsition sensor prnciucccj valuablc~ Iossons for futurw cornponont soloctic]n anti c@ificxdiorl. Issues of spacwflig}d heritage, ccWbc:nCfit/risk ass[!ssrriwit, mci ccmpcmnt spcmification m acickc:ssoci. It was fcmncl ttmt cc~stly sdwckllo ard budget overruns may km tmn avoickd if ttm capability c)f ttm canciichtc~ s~!rlsors to meet requirements had ken more critically exmirwci prior to freezing tho ck?sign. 1 ho use of Cngirmring rnockls anti mrly c@ificdion tests is also rc:comrrwtdeti. IN-I I{C)I)lJCYI ION Uncotnrnor] rc)tatic)rlat axis pc)intirlg acxwracy, fc)r a SAII, is roquirc!cl duo to tll[! ~jrccisiorl c)rt.)it Clc:tc!rrl-lirl:ltic)rl ([ 1 0[)) rc!c~tlir[!tllc:rlts on ttlc 'I 01'[ X/l IOSl l[lON spacwcrafl. '1 his infc)rtrmtiotl is vital to ttlc! prirnwy mission c)f tho spacmaft, wtlic:h is tc) survey the variatic)r] in cIcwar I Clcwatic]rl to an aczuracy c)f a few cx!rdimotors cwer ttle fmriocj of at k:ast tllroo ymrs. 'l Of 'F X/f 'OS[ ID(IN usos a sirlgk, very large scalar array ttmt acts m a sail in ttm solar wifld. 1 tm solar pressure! ar-lcj aerociyrmmic forms acting on tt-lo array causo mudl of tho total non-gravitational fc]rcc!s wtlidl must k accounteci for in the I'(ID prc)cms; if c)ric:ntatic)n of ttm array wittl respect to ttm satellite body is in errc)r, ttic! sc)lar [)rc:ssurc! anti aerc)clynarrtic form rtrcxkls will tw in orrc)r. '1 ho tc)tal c)rror allocatic)n from 1'()[) for ttm pitc}l, c)r rotatic)rd axis of tile SAD, is 5.G nlracj (0.3? C'),1 sigma, for all c!rror sourcms, induciing thc:rmally irducxci anti strudurd rrlisaligrlrnc! nts, " 1 hat mlount c)f c2rrc)r cc)rresponcis to a worst-case altitude c!rror c)f about 1 ml]. A 3-sigma acmracy rc!c]uirc!nwnt of 0.1 0 / 0 absolute Iirmuity was assigrwcj to ttw position sermor in th[! J)rc)ccss cjf allocating ttlc> ~)itcll axis c!rrc)r to all sources c)f urlccrtairlty. [Ricks Iligtl accuracy, corltinuous rotatiorl in cittwr dirwction is rwcmsary, wittl no interruption of signal, opc!ratirrg rate in fligtlt ccwlcj range: from zc!rc) tc] 110 rnracj (6.3(') por minute, but ccmld go rnucll Iligtlc:r in grounci test. 1 ifc:, irl torrns of total nunlbc)r of rcwoktions, was not a nlajc)r ck!sign cllalleng[! for any of the o~)tiorls wc studieci. An doctronic moans c)f switctlir~g bc;twcwn [)c)tc!rltiorlletc!r ([)c)t) [!lorrwnts to maintain continuous functic)n cmr …