ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
10:15 12:15 1:15 3:3O 3:45-4:30 5:30-10:30 4:45 5:30 6:00-7:00 7:00 10:00SESSION V-DEPLOY MarkCalassa, Session Chair Lockheed MartinSpaceSystems Company, Sunnyvale, CA •Landsat 7SolarArrayTesting Experiences DanielHelfrich, Goddard SpaceFlightCenter, Greenbelt, MD •Deployment Dynamics ofSolarArrayswithaLink-in-Slot Hinge/Latch Mechanism WalterDaniel,Mechanical Dynamics, Inc.,Austin,TX&G.Michael Bidinger, OrbitalSciences Corp.,Germantown, MD •Inflatable BoomControlled Deployment Mechanism fortheInflatable Sunshield InSpace(ISIS) FlightExperiment George SapnaIII,JohnFolke,Charles Sandy&DaveCardogan, ILCDover,Frededca, DE •ANovelMechanism usingShapeMemory AlloytoDriveSolarFlapsoftheINSAT-2E Satellite N.Viswanatha &T.Murali,IndianSpaceResearch Organisation Satellite Centre, Bangtadore, India LUNCH BREAK SESSION VI-POSITIONING/ANTENNA MECHANISMS SteveKoss,Session Chair NavalResearch Laboratory, Washington, D.C. •Evolution ofanActuator Family PaulStigell, PekkaKyrenius, TomiYlikorpi &KaiViherkanto, VTTAutomation, Finland •Coaxial CableFailureinaSpacecraft Mechanism Michael Chiu,TRWSpace&Technology Division, Redondo Beach,CA •TheSeaWinds Scatterometer Antenna Subsystem ontheQuikScat Spacecraft BrianWorkman, Honeywell Satellite Systems Operation, Glendale, AZ,&EricSchwartzbaum, JetPropulsion Laboratory, Pasadena, CA •Antenna Pointing Mechanism forSteerable SpotBeamAntennas Manfred Schmid, DaimlerChrysler Aerospace, DSS,Friedrichshafen, Germany DR.CHARLES COALE AWARD ANNOUNCEMENT BREAK SPECIAL PRESENTATION Mechanisms ontheNextGeneration SpaceTelescope JonLawrence, NASAGoddard SpaceFlightCenter SYMPOSIUM BANQUET ATB&ORAILROAD MUSEUM ShuttleforguestsleavesHoliday InnfortheGreenbelt Marriott BusesleaveGreenbelt Marriott parking lot Reception &Exhibits atB&ORailroad Museum Dinner&GuestSpeaker -TomHenricks: Mechanisms fromanAstronaut UserPointofView BusesleaveRailroad Museum andreturntothehotels X
FRIDAY, 12 7:00 8:00 10:30 10:45 11:15 11:30 12:30 1:00-4:00MAY2000 FridayPresenters' Breakfast SESSION VII-TRIBOLOGY &OTHER MECHANISMS Edward Devine, Session Chair Swales &Associates, Beltsville, MD •EarthScanner Bearing Accelerated LifeTest BrianDietz,Moog,Inc.,Chatsworth, CA,StevenVanDyk, Raytheon Systems Company, Santa Barbara, CA,andRoamer Predmore, NASAGoddard SpaceFlightCenter, Greenbelt, MD •Measurements ofFriction Coefficients between Oxidized andContaminated Surfaces in Vacuum andinAir PeterFrantz&Stephen Didziulis, TheAerospace Corporation, ElSegundo, CA •Marshall SpaceFlightCenterHighSpeedTurbopump Bearing TestRig Howard Gibson, ChipMoore&RobertThom,NASAMarshall SpaceFlightCenter, Huntsville, AL •Design, Development andTesting ofUmbilical System Mechanisms fortheX-33Advanced Technology Demonstrator AlanLittlefield &Gregory Melton, NASAKennedy SpaceCenter, Florida •Development ofaFlywheel forEnergyStorage andAttitude Control ofanExoatmospheric Interceptor DougHavenhill, SatCon Technology, Peoria,AZ;FrankNimblett, SteveNichols &JohnYoung, SatCon Technology, Cambridge, MA BREAK VIDEO PRESENTATION: AnOverview ofGSFC TECHNICAL SESSIONS CONCLUSION •PRESENTATION OFTHEHERZL AWARD •CLOSING REMARKS LUNCH BREAK ANDCHECK-OUT BUSES DEPART HOTEL FORGSFCTOUR GODDARD SPACE FLIGHT CENTER FACILITY TOUR xi
SYMPOSIUM ORGANIZING COMMITTEE Stewart C.Meyers, HostChairman, NASAGSFC StuartH.Loewenthal, General Chairman, Lockheed Martin Edward A.Boesiger, Operations Chairman, Lockheed Martin ObieH.Bradley, Jr.,NASALRC Michael JoEiden,ESA/ESTeC Carlton L.Foster, NASAMSFC Robert L.Fusaro, NASAGRC ClaefF.Hakun, NASAGSFC Christopher P.Hansen, NASAJSC AlanC.Littlefield, NASAKSC Edward C.Litty,JPL Ronald E.Mancini, NASAARC FredG.Martwick, NASAARC Martha E.Milton, NASAMSFC MinhPhan,NASAGSFC JohnF.Rogers, NASALRC William C.Schneider, NASAJSC Donald R.Sevilla, JPL JamesJ.Zakrajsek, NASAGRC SYMPOSIUM ADVISORY COMMITTEE H.Mervyn Briscoe, ESA/ESTeC (ret) DavidF.Engelbert, NASAARC(ret) OttoH.Fedor, Lockheed Martin(ret) Angelo Giovannetti, NASAARC(ret) JohnE.Harbison, NASAMSFC(ret) JohnW.Redmon, Sr.,NASAMSFC(ret) AlfredL.Rinaldo, Lockheed Martin(ret) Sterling W.Walker, NASAKSC(ret) Bowden W.Ward,Jr.,NASAGSFC(ret) Nathan D.Watson, NASALRC(ret) Edward A.Wegner, Lockheed Martin(ret) _di
Theredesignofthesensor(Figure12)wassubtlebutproducedmuchbetterresponse.Effectively, the onlychangewastosplitthecoilfromonelargecoilbetweenthepolesto2smallercoilsmoveduptothe facesofthepoles.ThecoilswerethenwiredinseriestoensurethataNorthandaSouthsurfacefaced eachotheracrossthegap.Theresultwasavastimprovement inresponse.Thefinaldesignofthe circuitreadsthechangeinreluctanceandisconvertedtoavoltageresponsescaledfrom1.25to3.75V fromopentoclosedposition,respectively. Conclusions TheIRACshuttermechanism provides precise, repeatable, limitedangular motionidealforinfrared sensing cryogenic instruments. Theuniquedesignoftheactuator enables theshuttertodissipate very lowpowerduringoperation. Thetorsionwiresuspension system iselegant initssimplicity andenables theshuttertobedesigned tofailopenandremainopenthrough subsequent attempts toclose.As designed, theshutterwillsurvive andoperate throughout allstagesoftheIRACmission andremain operable inthepost-cryogen environment ofthespacecraft. Finally, theinclusion ofacontinuous variable reluctance sensorenables theshuttercontroltobeoptimized andensures theknowledge ofthe mirrorduringatroubleshooting operation. Theshutter meetsorexceeds allfunctional andscience requirements andistheresultofthededication ofatalented development team. Acknowledgements SidJohnson -mechanical design, assembly, test George Reinhardt --magnetic analysis, sensordesign Chiachung Lee-mechanical analysis TomHanyok, BryanGrammer- mechanical design, drafting CarlosLugo,CarlosBernabe, GaryBrown-electronics design, test OtherContributors WillieBarber, WillieBlanco, DerickFuller,PaulHaney, SteveHendricks, DanMcHugh, DavePfenning, JimTowers, SteveWood References 1.IRACProject. "Infrared ArrayCamera (IRAC)Critical Design Review Package." Goddard Space FlightCenter, July,1998. 2.Fazio,Giovanni G."SIRTF Infrared ArrayCamera, IRACScience Requirements." Smithsonian Astrophysical Observatory (January 1998),p.1. 3.Miles,JohnW.andDanWTrites. "Space Infrared telescope Facility, Observatory Performance and Interface Control Document." Lockheed Martin,November, 1998. 4.Fazio,Giovanni G."SIRTF Infrared ArrayCamera, Instrument Performance Requirements Document." Smithsonian Astrophysical Observatory, March22,1999. 5.Carpenter SteelDivision. "AlloyData:Hiperco Alloy50A."Carpenter Technology Corporation 6.Reed,Richard P.andAlanF.Clark,Ed.Materials atLowTemperatures. American Society for Metals, MetalsPark,Ohio©1983,pp.94-100. 7.Anderson, Richard H.andSidney B.Bernstein. "Scanning MirrorforInfrared Sensors." Lockheed Missiles andSpaceCo.,Sunnyvale, CA.,7thAerospace Mechanisms Symposium, Houston, Texas, 1972 8.Touloukian, Y.S.,R.K.Kirby,R.E.Taylor,andP.D.Desai. Thermophysical Properties ofMatter, VoL12:Thermal Expansion, Metallic Elements andAIIoys. Plenum Publishing Corporation, ©1975. 10
PICKOFF MIRROR MIC ALIGNMENT PLATE SHUTTER TRANSMISSION CALIBRATOR OPTICAL • HOUSING FPA4 FPA2 Figure1-IRACAssembly MirrorClosed EndkCap Metrology \ \ Cube _../,_ . Temperature \_._._._._._._\ ///_//_ Connector Housing MirrorOpen Figure2-IRACFlightShutterUnit Figure3-EndViewShowing MirrorAngle 11
Electromagnetic Coil • _ EndCap /CloseoutRe -%  .otoj ==0r/\_=.=.o_Counterweight ShaftHub Figure4-Shutter CrossSection Mirror Actuator I Ramp "_""_rL t__ ,/_ Closeout /Stator ,_'/0_ Metrology Cube Con/", _00_.-- Connectc-r Bracket SpringPreload Ring//_/4,__,0_TM w..s,r,.°.'I/"\Nut/ Retainer Temperature Sensor Figure5-Shutter Exploded View Flexure End Threaded Piece(SideCross-section) Flexure Flexure Hub Cross-section \c'x// (FrontView) MtrrorMounting Surface Figure6-ShaftSubassembly 12
Stator  otor  / Stator Latching Tab ___Closeout Electromagnetic Coil 3.8 36 3.4 _-3.2O 2.8 P_(:: 2.5 24 2.2'Figure7-Actuator Exploded View IRACShutter Sensor TestData&2ndOrderCurveFit ', : : : : ', ,, iii!ii: ........._........i........_........_........_........i........b-J--- / ........._........_........i........i........_........_....----,_/----- ......... ;......... ;......... _......... _......... ,........ ,....... ,........ ......... •........ •........ •........ _........ ,....... ,........ ,........ i I I I t i I 5 10 15 20 25 30 35 40 Shutter Angle (degrees) Figure8-IRACSensor Response vs.MirrorAngle 6O 5O 40 t_ =_30¢J o •20 lO 5 10 15 20 25 30 35 Mirror Angle (degrees) Figure9-Current vs.Measured MirrorAngle40 13
10430 100, e- =- E 10'I_Excess Torque [In-oz) ISpringTorque (in-oz) MotorTorc_ue _n-oz) 1 = , i i i i i 5 10 15 20 25 30 35 40 Mirror Angle (deg) FigurelO -Spring, Motor, andExcess MotorTorques at60mA ! IE1000 100 I0 0.1•J'--0degrees 4degrees _9degrees "R'-14 degrees "-_-19 degrees _24degrees _29 degrees "P'34 degreesA J ,L Motor Current (mA) Figure 11-Excess MotorTorque vs.Current forVarious MirrorAngles Electromagnetic =/ Coil Wires _:____ (toconnector) i2 jBracket Wire / (toconnector) _ ==__,,Electromagnetic "iH_i _'_-_'_ Coi, !,!!! -_, ----_ -"= Electromagnetic _i_ Coil .w,re(toconnector) OldConf_uration Figure12-Position Sensor Designs 14
rightsideofthephotograph. Thelinearactuatorsarethecartridgesextendingfromthetopandbottomof therotaryactuatorcase. Actuator Torque Requirement Theoutputtorquerequired fromthedooractuator wasalmostentirely drivenbytheexpected stiction that coulddevelop intheO-ringdoorseal.Across-section ofthemechanism isshowninFigure2andshows theopenandcloseddoorconfigurations. Thetwobarlinkage applies around 222N(50Ibf)offorce(1.8 N-mor16in-lb)outputtorquefromtherotaryactuator) totheO-ringsealwheninthestraightened position. Thisforceisrequired tocompress theO-ringsufficiently sothatthedetector assembly canbe evacuated. Themechanism itselfconsists ofthealuminum door,dryTorlonbushings inallrotating joints, titanium/aluminum linkages, thetitanium collimator, aluminum sealretainer andthe15-5ph stainless steel linkage driveshaft. Theslip-fitTorlonbushings allhaveredundant moving interfaces whichwouldstill allowrotation ifoneofthesurfaces weretobind.Running torqueforthemechanism wasverylow,even in1Genvironments, sincethedoorweighs onlyabout0.11kgm(0.25Ib).Thetotalrunning torqueforthe drivetrainwasonlyaround 0.5N-m(4.5in-lb),whichwasmostlythefrictional andspringlossesinside therotaryactuator. Thefrictional lossesintheTorlonbushings wereminimal. Analysis andtesting showed thattherewasnotanissuewithclearance changes whichcouldresultinanybinding of mechanism components, evenatthemostextreme temperatures withintheoperational range. Collimatqli .L___L, I'r_ i I O-rin_Seal SealRetaineri C._),,_O IiDoorO en  ] 2BarL r-----Jl DoorClosed _. _/"r_, I  .... Ir,i-tm---xr'-'-r---'-_ I/I, II  ,l!jL_ I Figure2-ACISDoorMechanism 18
atmosphere ofpressuredifferentialprovidesabout500poundsofclosingforceonthedoor.Therefore oncethedoorsealed,apositivelatchwasnotnecessaryandtheinstrument couldbehandledsafely withoutthefearofdamagetothefocalplaneandOBFs. DuringthenextseveraldaysChandrawasremovedfromthechamber,theISIMwasremovedfromthe opticalbenchandpartiallydisassembeled, thentheACISwasremovedforshipmentbacktoLockheed Martin.Initialexternalinspections atTRWlookednormalexceptthatthedoordidappeartohavemetal tometalcontactwiththesealretainer.Thismetal-to-metal contactcouldsupportthecoldwelding hypothesisbutlaterinspections andtestingwoulddiscountthisfailuremode.TheACISdetectorwas thenshippedbacktoLockheedMartinwhereinspections anddisassembly couldoccurinaclass100 cleanroom. A.Door/Seal RetainerBound •Coldweld •Ice •SealAdhesion Electrostatic Diffusion VanDerWaals Chemical Bonding B.RotaryActuator Bound •PartsBound •Mismatched parts •Contamination C.ParaffinActuatorBoundorFailed •Heaterfailed •Waxleak •Startlowtemp •Lowlube D.RotaryActuatorShearDiskPreviously Ruptured ETestProcedure notfollowed F.Retarding Torque•6.8Nm(60in-lbs.) •Over-center •SealSeparation G.Unkages Bound •CTEMismatch •Bushing/Linkage bending •Ice •Contamination Figure3-ACISDoorFailure FaultTree In.itia!Inspections atLockheed Martin Failureinvestigation effortscentered around closingbranches ofthefaulttreeshowninFigure3.Initial inspections ofthedoormechanism atLockheed Martindidnotrevealthecauseofthefailure.Alllinkages appeared tobefreeandthetwobarlinkwasslightly over-center, whichexplained whythedoorwasable toseal.Itappeared thatthedoorwasmetaltometalwiththesealretainer, butuntilthedetector wasrepressurized, wewouldnotknowifthedoorandsealwereboundtooneanother. Sincetherewasstilla vacuum insidethedetector, asmeasured withtheVacuum Ground Support Equipment (VGSE), we elected toremove theSTARSYS actuator priortodetector housing re-pressurization, sothatitcouldbe inspected independently oftherestofthemechanism. DoorSeal/Retainer Bound(FaulttreeItemA_ Sincecoldwelding ofthegoldplateddoortothealuminum sealretainer wasapossible failuremode, extreme carewastakenasthedetector assembly wasre-pressurized. Dialindicators weremounted 22
12.0 100 nc_ net N4o 2O 0DoorPot,.ngle AotTemp DoorlS C.J,_.ED DoorNO-ICLOSED DoorISC_'EN HeatON CloseActTemp CLOSE SV OPEN SW\\ I I i i i _ i i ! 21 2.2 Time(hrs day220)\ t \L 4,t , I 23 Figure4-On-Orbit ACISDoorOpening wehadoperated thedoormechanism asplanned, thedoormayhaveopened andwewouldnothave hadtodealwiththelongandinvolved failureinvestigation. Ifithadfailedduringtest,thefaulttreewould havebeenmuchsimpler sincewewouldnothavetodealwithissuesrelatedtocoldoperation. One positive contribution, however, wasthedevelopment ofamuchsafer,morereliable operational procedure thatultimately wouldcontribute toasuccessful dooropening on-orbit. Another lessonisthateitherthemechanism designoroperational procedure shouldallowforaprolonged stallcondition tooccur,duetopossible binding orstiction, without mechanism component failure. Inthe ACISdoorapplication, duetothelateoccurrence ofthefailure,theprogram successfully adopted an operational technique topreclude afailureduetoastalledcondition, andalsodeveloped atechnique to remove thecauseofthestall. TheresultsoftheACISdoorfailureinvestigation ultimately wereinconclusive andthusveryfrustrating. Thespecific causeofthetestfailurewasneverpositively identified, although several potential causes wereleftopenaspossible. Asitbecame clearthatthespecific causemightnotbeidentified, mucheffort wasputinto"mitigation procedures". Theseprocedures weredeveloped to"mitigate", ortoreducethe effectof,possible failuremechanisms suchasO-ringstiction. Theseprocedures wereextensively tested onACISdoorengineering models, andlaterontheflightunititself. Acknowledaements TheworkatSAOwassupported byNASAChandra contract NAS8-39073. TheworkatLockheed Martin wasperformed underMITcontract SC-A-124624 28
- MECA Figure 1-Mars2001Lander Figure 1isanartist's rendition oftheMars2001Lander showing thelocation oftheMECA experiment enclosure ontheLander deck.TheMECA WetChemistry Laboratory consists offouridentical (redundant) experiment cells.Figure 2shows aphotograph andschematic viewofoneofthefourcells. Inthebottom portion ofeachcellisa"beaker" where theexperiment measurements takeplace. Inthe upperportion ofthecellarethesample handling anddelivery mechanisms (thesubject ofthispaper). Fourflightunits,aqualification unit,andafielddemonstration unitweredesigned, manufactured, tested anddelivered toNASA JPLoverthecourse ofan18-month program thatwascompleted July1999.  /Stirring Reagent .._'*'-_ Mechanism Dispenser._ _" _ | _%._ _ Water Drawer _)_ ,.."_,__ Tank Swit Drawer /_ Tank Actuator Actuator Figure 2-MECA WetChemistry Laboratory 30
TheMECAWetChemistry Laboratory mechanisms perform thefollowing functions: 1.SoilSample Measurement andDelivery 2.WaterStorage andDelivery 3.Reagent Delivery 4.Stirring SoilDelivery Thesoildelivery system hasthefollowing requirements: •Accept ascoopofMartian soilfromtheLanderrobotarm. •Measure a1+0.1ccsoilsample. •Deliverthesoilsample totheexperiment beaker. •Provide ameansforindicating successful acceptance anddelivery ofthesoilsample. •Allowforupto16degrees oftiltinanydirection. •Workwithintheenvelope andmassconstraints ofthesystem. •Maintain system sealing requirements forleakage oflessthan1cctotalwaterlossthroughout cruiseandlessthan0.1cc/daywaterlossthroughout theexperiment. •Survive launch, cruiseandlanding environments. •Operate inthepresence offrost. Across-section ofthefinaldesignisshowninFigure3. Actuator Return Pressure Sensor Spring Seals Actuator Bellows SoilCavityParaffin Drawer Movement 4(------ DrawerParaffin Actuator OutputShaf{ Housin (sealed)I _1( DeliveryScoop SoilToBeaker (incorrectly showninclosedposition) (Beakernotshown) Figure3-SoilDelivery System Thesystem consists ofthefollowing components: •Sample Delivery Drawer •Paraffin Actuator •ReturnSpring •Brush •Scraper•O-ringSeals •Extension LimitSwitch •Extension Telemetry Switch •Retraction Telemetry Switch 31
functionproperly.Thesealswithlighterspringsdidnothaveenoughcompliance topreventleakageona surfacethathadbeenscratchedbyparticlesofgritorsoil.Astandardo-ringsealalsohadtoomuch frictiontoallowthedrawertofunctionproperly. Tocomplicate matters,changesduringthecourseoftheprogramplacedmuchmorestringent requirements ontheseals.First,itwasdiscoveredthattheion-specific electrodesensorsinthewallof thebeakeraresensitivetodryingout.Itisthereforedesirabletoholdsomenominalamountofwaterin thebeakerthroughoutcruisetokeepthesensorsmoist.Inadditionitwasdiscoveredthatthesensors aresensitivetorapidchangesinpressure.Thismeanttheexperiment chambershoulddepressurize somewhatgradually,ifpossible,ratherthanabruptly"popping"open. Thebestsolutionturnedouttobeano-ring-typesealwithsignificantly reducedsqueeze.O-ringsprovide enoughcompliance tosealaroundmicro-scratches andparticles.Thelightsqueezereducedfriction allowingthedrawertoretractwiththeforceoftheexistingspring.Inaddition,auniquecombination scraperandfloatingwasherwasusedtoincreasecompression ontheo-ringandthereforeprovide additionalsqueezeattheveryendofstroke.Protrusions ontheoutsidediameterofthedrawercatchthe scraper/washer pullingitinwardandcompressing theo-ringsealintheaxialdirectionasthedrawer finishesitsreturnstroke.Becauseoftheresilienceoftheelastomermaterial,someoftheaxial compression isconvertedintoradialcompression, whichimprovestheseal.Thisarrangement provedto beeffective enough tomeetthecruisesealing requirement. Longtermtestingoverthecourseofseveral weeksshowed anextrapolated totalleakoflessthan0.4ccofwateroverthe9-10monthcruise. The sealswerealsoeffective afterrepeated soildelivery cyclesusingvarious gradesofsandandsimulated Martian soil. WaterStorage andDelivery TheWaterStorage andDelivery System hasthefollowing requirements: •Transport 32cc'sofwatersolution fromEarthtothesurface ofMars. •Onceonthesurface, deliverthewatersolution totheexperiment beaker. •Maintain system sealing requirements forleakage oflessthan1cctotalwaterlossthroughout cruiseandlessthan0.1cc/daywaterlossthroughout theexperiment. •Operate inthepresence offrost. •Allowforupto16degrees oftiltinanydirection. •Workwithintheenvelope andmassconstraints ofthesystem. TheWaterDelivery System (Figure 4)consists ofthefollowing components: •WaterTank •TankSealPuncture Actuator •TankSealPuncture Needle •TankSwitch •TankHeaters •TankRTD Thewatertankisahermetically sealedwelded titanium container. Theshapeofthecontainer isdictated bythedesiretodispense thewaterintothebeakerusinggravityandbytheconfines oftheavailable space.Atthestartoftheexperiment thewaterinthetankisfrozen.Heaters bonded tothewallsofthe tanksupplyheattomelttheice.Aparaffin actuator isthenusedtopuncture asealdiscatthebaseofthe tank.Thewaterthenflowsthrough thehollowpuncture needle, thenthrough anarrowpassage intothe beaker. Handling waterinthelowpressure Martian atmosphere isnotasstraight forward asonemightfirst imagine. Theambient pressure onMarsis6-10Torr,approximately ahundred timeslessthanthe atmospheric pressure onEarth.Thereduced pressure suppresses theboilingpointofwaterwhileleaving 33
WaterTank __-_ _Actuator PunctureNeedle__ OutputShaft WatertoBeaker Figure4-WaterDelivery System thefreezing pointunchanged. Watercannotexistasaliquidatpressures below4.5Torr-icesublimates directly towatervaporandthevaporcondenses directly tofrost.At6Torr,waterboilsatatemperature ofonly3.5°C. Thisleavesaverynarrowrangeoftemperatures forliquidwaterandalthough itis conceivable toconduct theexperiment withinthiswindow, theuncertainties inthermal controland barometric pressure preclude thisapproach. Thealternative istoconduct theexperiment inaclosedcell thatissealedfromtheatmosphere. Thesealintegrity mustbegoodenough toallowinternal pressure to buildwithinthecellifthetemperature increases. Thesealmustbemaintained throughout theexperiment andwhenever thereisliquidwaterinthecell. Another problem wasdetermining themostfavorable designapproach forstoringwateroverextended periods oftemperature andpressure fluctuations, andthenallowing ameansfordelivery ofthewatertoa different container. Someofthetradesinvestigated duringthedesignphaseincluded comparisons of solidtanksvs.flexiblewaterbags,andsolenoid valvesvs.puncture valves. Awelded tankwithametal discandc-ringsealwaschosen asthebestmethod fortransporting thewateroverthelongcruiseto Marswithout leakage (leakrate<10-7scclsec helium). Flexible waterbagsinavacuum environment wereconsidered toorisky. Apuncture needledrivenbyaparaffin actuator provided ahighlyreliable meansofpuncturing themetal sealdisc.Paraffin actuators arewellsuitedtothistaskbecause theyprovide ampleforceinasmall package withhighreliability. Various discmaterials, thickness andcoatings weretried.Harder materials suchasstainless steelandtitanium required eithertoomuchforceoruncomfortably thinmaterial thickness. Thefinaldesignuseda0.38-mm (0.015-inch) thick,1045Aluminum disccoatedwithFEP. Puncture required approximately 5.4N(24lbf).Lateintheprogram therewereindications ofcorrosion in oneofthetests.Speculation thattheFEPcoating ofthatparticular discmayhavebeendamaged and therefore allowed agalvanic coupletosetupbetween thetitanium tankandthealuminum disc.The corrosion couldneverberepeated orconfirmed andadesignchange wasdeemed unnecessary. Oncethetankconfiguration andsealpuncture method wereset,theproblem ofdispensing thewater through asmallpuncture holeatthebottomofthetankwasaddressed. Ifthereisonlyasinglesmall holeatthebottomofacontainer fulloffluid,surface tension canprevent thefluidfromexitingthrough the hole.Whensomeofthefluiddoescomeoutatemporary vacuum canbecreated inthetopofthe container exacerbating theproblem. ThelowergravityonMars(onlyabout1/3thatofEarth)makesthe problem worsebyreducing thepressure headavailable tobreakthesurface tension. Therearea 34
accomplish thetask,amotordrivensystemwaschosenbecauseitisthemosteffectiveandversatileand alsobecauseitcouldfitintheavailablespace(Figure6). Paraffin _ ,. '1/ Figure 5-Reagent Dispenser ! Beaker notshownShaftSealsStirMotor Impeller Figure6-Stirring Mechanism Thestirringmechanism hasasmallimpeller thatextends downintothebeaker. Theimpeller shaftis drivendirectly byaMicro-Mo miniature coreless d.c.motor.Themotorhasprecision ballbearings and vacuum-compatible lubrication forspaceapplication. Themotorno-load speedasspecified bythe manufacturer was16,000rpm.Thespeedwasreduced andtorqueincreased bya64:1planetary 36