limitedwearwasobserved ontheballsandraces.Darkdeposits ofleadorleadnapthanate werenot visible, indicating theleadnapthanate remained dissolved inPennzane after209millionrevolutions at 45°C.Thisformulation ofPennzane performed verywellathightemperature andintheboundary lubrication regime. Thelubricant andbearing surfaces havebeenanalyzed usingmicro-Raman, microFTIR,XPS,SEMandSECandtheresultssummarized. Comparison ofthebearing wearandthelubricant degradation afterlifetestingat23°Cand45°C,clearly demonstrated thatthesevere bearing damage foundinthe37°Caccelerated lifetestoriginated froma thermal controlfailure. Thisdrovethebearing testtemperature wellabove90°C,assuggested inthe Reference 1. Aswithmostlong-life lubricated mechanisms, lubrication life,bearing precision, anddynamic performance arethecriticalfactorsintheoperation ofthescanmotor/encoder. Asafirstphaseoflubricant selection for MODIS, bearings werelubricated withseveral candidate lubricants, accelerated lifetestsperformed, and resultsevaluated. Asynthetic hydrocarbon, Pennzane SHF-X-2000 with2.5%leadnapthanate and0.6% antioxidant additives, wasselected. Thesecond phaseoflubricant selection consisted ofthreelubricant lifetests.Theseresultswerereported inRef.1andinthispaper.Thethirdphasewasthesuccessful qualification lifetestofthescanmotor/encoder mechanism. Threebearing teststations wereconstructed toevaluate thelifeofPennzane lubricant fortheMODIS opticalscanmechanism. Five-flight qualityscanmotor/encoder mechanisms werefabricated, assembled andtested. Theengineering modelwasusedtodevelop theopticalscanning control system. Thesecond mechanism wasusedforqualification lifetestingandhassuccessfully completed thattesting. Thethird mechanism wasflownintheMODIS instrument ontheTERRA satellite. Thefourthmechanism willbe flownintheMODIS instrument ontheAQUAsatellite laterthisyear.Thefifthmechanism remains asa spare. Eachscanmotor/encoder mechanism contains twoduplexbearing pairsdrivenbyabrushless dc-motor. Pennzane SHF-X-2000 isasynthetic hydrocarbon lubricant andwaschosen forthebearings and mechanism. Tomitigate instrument risk,bothaccelerated andoperational speed lifetesting were conducted inparallel withthemechanism designandfabrication inordertoverifythelubricant lifeearly enough intheprogram toswitchlubricants forMODIS ifaccelerated testingrevealed earlyanomalies. Accelerated andReal-Time Pennzane LifeTestMethod Ineachteststation, threeflightquality, 440Csteel,66.675-mm (2.625-inch) outerdiameter, 50.800-mm (2-inch) innerdiameter, DFduplex pairbearings witha165-N(37-pound) preload wereused.The bearings, phenolic laminate retainers, andsintered nylonreservoirs werelubricated inaccordance with flightrequirements. Theteststationisillustrated asFigure1.Eachbearing pairwascontained initsown clamp/housing. Thehousings alsocontained lubricant reservoirs. Station IIandIIIhousings werefitted withinnerandouterraceheaters. Astraingaugewasmounted onacantilever beamsupporting each bearing enclosure tomeasure thetorque. Theinnerracesofthreeduplexpairsweredrivenbyacommon driveshaft.Instantaneous torquereadings wererecorded every15minutes. Themonthly average ofthese readings wasplotted overthelifeofthetest(seeFigure 2).Onetelemetry platinum resistance thermometer (PRT)wasmounted toeachbearing outerracehousing. TwocontrolPRTs(Stations IIand IIIonly)werealsomounted toeachbearing housing (oneontheouterraceandonefortheinnerrace).All testing wasperformed undervacuum. Although allthePennzane lubricant wastestedintheboundary lubrication regime, theacceleration factorwasestablished assimilarcalculated specific filmthickness (_,) inallthree-test stations. Thismethod wasusedasanarbitrary wayofcreating anaccelerated lubrication lifetest.Threeduplexpairsofbearings weretestedinStation IIat72RPMand45°C,inStation IIIat50 RPMand37°Cand22°CandinStation IVat20.3RPMand23°C.