Theactuatorsdeveloped fortheNanorover are10millimeter, brushlessdcmotorswithaplanetary gearbox.Theactuatorsarecapableoflastingover100millionrevolutions inacryogenicenvironment. Rotorpositionsensingwasnotinitiallyincludedinthemotordesignbecauseback-EMFsensingfor commutation wasconsidered. Failuremodesofthesystemledtotherequirement forunpowered, static rotorpositionsensingofthemotorsandahallsensorassemblywasaddedtothemotors.Allofthe motorizedmechanisms (10ontheNanoroverandtwoontheOMRE)usedthissameactuator. Nanorover Electronics Theelectronics fortheNanorover aresignificantly morecapable thantheMarsPathfinder Sojourner rover.WhiletheSojourner roverhadbatteries tokeepthememory aliveandtheelectronics warm throughout thenight,theNanorover hasnospaceforsuchluxuries. Whenthesungoesdownonthe Nanorover, allfunctions cease. TheNanorover usesElectrically Erasable Programmable ReadOnly Memory (EEPROM) tostoreallofitscodeandovernight variables. Anydatacollected duringtheday mustbedownloaded totheMUSES Cspacecraft orlost.Theelectronics alsocontains alargegatearray thatperforms manyofthehardwired functions. Thesefunctions include communications decoding, motor commutation andcontrol, datarouting andswitching. Theelectronics system alsocontains ananalog signalchainthatprovides theAnalog-to-Digital conversion oftheinstrument data,temperature data,and engineering telemetry. Additional functions oftheelectronics system include powerconditioning, power distribution, andmotordriveamplifiers. SincetheNanorover startsfunctioning assoonasthesunlight onthesolarpanelsissufficient toinitialize thecomputer, theelectronics assembly hastooperate atthetemperature extremes oftheNanorover components. Theselection ofelectronic components thatwillfunction properly atthetemperature extremes isverylimited. Thecoldextreme isthedefining temperature. Noneofthesuppliers ofthe electronic components wouldratetheirdevices atthelowtemperature, soalargeamount oftestingwas required toidentify electronic partsthatwouldproperly function at-185°C. Theelectronics system wasallocated averysmallvolume intheNanorover ononesideoftheoptical bench. Thelargerangeoffunctions combined withthesmallavailable volume ledtoanelectronic packaging design basedonchip-on-board technology. Thecircuitboards aremadefromstandard polyimide-glass material. Thesiliconismounted directly tothepolyimide boards andbondwiresare routedfromthepadsonthesiliconchipstopadsontheboards. Thismethod eliminates theadditional partpackage normally usedinstandard electronic packaging designs. Themajorbenefit forthe Nanorover wasasignificantly reduced volume forelectronic components and,because lessboardarea wasrequired, significantly reduced massfortheassembly. Themostcommon method ofprotecting the chip-on-board assembly istocoveralloftheintegrated circuits andtheirwirestothecircuitboardwitha polymer covering. Thepolymer hasthesamemassastheboardmaterial (sanscopper) andrepresented asignificant massincrease. Thefinaldesign usedthechip-on-board assembly without thepolymeric covering, leaving the0.1-millimeter diameter bondwiresexposed. Thisapproach required theuseof handling fixtures duetothefragilenatureoftheassembly priortocompletion ofthefinalassembly. Thechip-on-board assembly packaging technique alsometthelargetemperature rangerequirements of theNanorover component assemblies. Inaddition tosurviving thetemperature extremes, thepackaging designalsosurvived thethermal cyclingrequirement of100cyclesofthefulltemperature range. NASA/CP--2002-211506 109