Designing Spacecraft Mechanisms forSand,Dust,WaterandFrost KurtLankford" Abstract Thispaperdiscusses thedesigntradesandlessons learned inthedevelopment ofamechanisms package fortheMarsEnvironmental Compatibility Assessment (MECA) WetChemistry Laboratory (WCL), anexperiment ontheMars2001Surveyor Lander. TheWCLperforms in-situwetchemistry experiments onsamples ofMartian soil.Designing mechanisms tohandleMartian soilalongwithwater andfrostposedchallenges thataresomewhat uniqueandforeigntothespacecraft mechanisms industry. Lessons learned inthedevelopment, manufacturing andtestingofthevarious components including the waterstorage vessel, soilandreagent delivery mechanisms, stirringmechanism, seals,actuators, clearances, andpackaging ofthesemechanisms arediscussed. Introduction Inrecentyears,NASAhasre-emphasized theexploration ofoursolarsystem. Thishasledtoan ambitious seriesofexploratory missions tothesurface ofMars.Thedesiretoinitiallyuseunmanned landerprobestoinvestigate theplanethasplaceduniquenewrequirements onthedesigners of spacecraft hardware. Themechanisms designed forthesemissions mustoperate remotely inapoorly defined environment thatincludes gritanddust,alow-pressure carbondioxide atmosphere, relatively coldambient temperatures, reduced gravity, andinthecaseofthesubject mechanism, waterandMartian soil.Thispaperdescribes someoftheissues,trade-offs, pitfallsandlessons learned overthecourseofa faster,better,cheaper program todesignandmanufacture amultifunction flightmechanism forthese conditions. Specific designchallenges included measuring anddelivering arelatively unknown butpresumably dusty, grittysample ofMartian soilthrough asealedinterface. Another significant challenge involved storing waterthrough anine-month cruisetoMars,thendispensing ittoadifferent container andkeeping the entireapparatus sealedfromthelow-pressure Marssurface environment. Howdoesonedesignandtest aprecision spacecraft mechanism foroperation indust,gritwaterandfrost?Howdoesonemaintain effective sealsundertheseconditions? Whatstepsarerequired toperform anexperiment usingwateron thesurface ofMars.Thesetypesofdesignquestions arerelatively unknown tothespacemechanisms industry andpresented significant challenges tothedesigners ofthesemechanisms. TheMECAWetChemistry Laboratory The2001MarsSurveyor Lander includes amulti-faceted instrument calledMECA(MarsEnvironmental Compatibility Assessment). MECAisasuiteofexperiments thataredesigned toassess thecomposition, reactivity, andphysical characteristics ofMartian soil.Thepurpose istoassess thehazards facedby manned andunmanned mission equipment intheMartian environment. OneoftheMECAexperiments is aWetChemistry Laboratory. TheWetChemistry Laboratory isdesigned tomeasure andquantify the composition ofMartian soilandassess theinteractions between waterandtheMartian environment through simple, water-based chemistry. Thistypeofevaluation allowsfordirectcomparison withresults fromterrestrial-based soilsamples. Thespecific function oftheWetChemistry Laboratory thenisto perform anin-situ"benchtop" wetchemistry soilexperiment onMars.Themechanisms thatprovide sample delivery, watertransport anddelivery, reagent delivery, andstirringfortheMECAWetChemistry Laboratory arethesubject ofthispaper. *Starsys Research Corporation, Boulder, CO Proceedings ofthe34_Aerospace Mechanisms Symposium, Goddard SpaceFlightCenter,May10-12,2000 29