ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Thefirstinformation givenbytheseresultsisthatthesteelmarksareobservedwhenthepressure reaches4300MPawhateverthepreloadis.Whenthecontactpressureiscloseto4200MPa,itseems thatthehigherthepreloadis,theweakerthemarksare. Finally,thelastinformation isgivenbythebearingn°14.Whenthepressureisclosetotheallowable ECSSvalue,therearenovisiblemarks,evenwithagappingamplitudeof46pm.Thisbearing14has beentestedwiththetorque-meter andnospikehasbeenfoundoveronewholerevolution. Conclusion ThisworkdedicatedonMoS2drylubricatedbearingresistancetodynamicstressesinducedbyasatellite launchleadsustothefollowingconclusions thatprobablyneedtobecrosscheckedwithothertests resultsondifferentbearingsgeometryandsize. Abouttheinfluenceofthegeometry(firstquestionoftheintroduction): Themaximumcontactpressuregivenbyasoftware-based ontheHertziantheorybecomes pessimistic whenthecontactellipseangleisgreaterthan35°.Thisisprobablythereasonwhy thebearingswithaconformitysmallerthan1.05exhibitnosteelmarksevenwithaveryhigh predictedstress. Thedesignerhastotakecareofthegrooveedgethatcouldbereachedduringthedynamic vibrationsleadingtoatruncatedellipseandtoariskofanearlybearingdegradation. Thisriskis notalwaystakenintoaccountbythesoftwarecomputation. Whentheellipseangleisnotgreaterthan35°andforabearinghardnessof61HRc,thereisa verygoodcorrelationbetweenthe4200MPatheoreticalstressandthefirstappearance ofsteel indentation onthebearingraceways. AboutthepressurelimitationduetoMoS2(secondquestionoftheintroduction): AlthoughthefrictiontorqueisalwaysnoisierafteravibrationtestduetosomeMoS2particles releasing,therearenospikesinthefrictiontorquewhenthecontactpressureisnotgreaterthan 3500MPa.TheMoS2coatingisthenabletoresisttothemaximumECSSallowablecontact pressure. Whenthepressurereaches4200MPa,therearespikesinthetorquemeasurement andsome indentations inthesteel.Arun-intestmakesthespikesmuchlower,showingthattheMoS2 isstill abletolubricate thebearing, andthattheindents areoutside theballtracks. Aboutthegapping amplitude influence (thirdquestion oftheintroduction): Agapping amplitude greater than30pmdoesnotimplyasteeldegradation dueto"hammering". Thesteelindentismuchmoregoverned bythemaximum contact pressure thanbythegapping amplitude. However, whenplasticdeformation occurs, itseems thatahighgapping amplitude worsens theindents. References 1 Harris,T.A.Rolling Bearing Analysis Lewis,S.D.-Observations ontheinfluence oflaunchvibration onbearing torqueandlubricant performance -9thEuropean SpaceMechanisms andTribology Symposium. Li@geBelgium - September 2001 NASA/CP--2002-211506 330
product(commercially calledPennzane® Synthesized Hydrocarbon FluidX-1000,orsimplyX-1000)has nowbeenproduced.Ithasamoreusefullowtemperature viscosity(29,000cPat-40°C)andyetretains relativelylowvaporpressureatroomtemperature. Theobjectiveofthisworkistocompilesomeofthephysicalandtribological propertiesofinterestto spacemechanism designersforthisdisubstituted product(X-1000).Propertiesreportedinclude:wear ratesandrelativelifetimeinultrahighvacuumandtypicalphysicalproperties(i.e.,viscosity-temperature, pourpoint,flashandfirepoint,specificgravity,refractiveindex,thermalproperties,vaporpressureand volatility). Physical Properties Themeasured physical properties ofbis(2-octyldodecyl)cyclopentane, Pennzane ®X-1000, aregivenin Table1alongwiththecorresponding properties oftris(2-octyldodecyl)cyclopentane, Pennzane ®X-2000, andalinearperfluropolyalkylether (PFPAE). Forthehydrocarbons, theproperties reported wereobtained byASTMtestprocedures atthePennzoiI-Quaker StateTechnology Center, TheWoodlands, TX,except thatthermal conductivity, specific heat,andautoignition temperature wereobtained fromPhoenix Laboratories, Chicago, IL,andoutgassing datafromBallAerospace, Boulder, CO.Thedataforalinear PFPAE arefromtheliterature. VaporPressure Thevaporpressure ofPennzane ®SHFX-1000 wascalculated fromtherateofeffusion through asmall orificeinaKnudsen cell.At125°C, thevaporpressure is6x106Torr.Knudsen cellmeasurements [Nguyen andJones,2001]onaprevious lotofX-IO00 yielded asomewhat highervaporpressure of2.5x 10.5Torrat100°C. However, extrapolated to25°C,thevaporpressure isonlyabout3x10.9Torr. Theverylowvaporpressure andpourpoint(-52°C) ofbis(2-octyldodecyl)cyclopentane, Pennzane ¢X1000,arethesamecombination ofproperties thathavemadePennzane ®X-2000 sousefulforlubrication inspacecraft. Takentogether theydefineawide,usefultemperature rangeforX-1000 forvacuum applications. Viscosity Theviscosity indexofPennzane ®X-1000 ishigh(131)andthekinematic viscosity of9.4cStat100°Cis lessthanmightbeexpected fromsuchanon-volatile fluid.Inlinewiththelowvaporpressure, bis(2octyldodecyl)cyclopentane hasahighflashpointof290°C(550°F). Thermal Properties Thespecific heatofbis(2-octyldodecyl)cyclopentane is0.46cal/gmat30°C,about10%lowerthanthatof tris(2-octyldodecyl)cyclopentane. Fortemperatures between 30°Cand100°C,thespecific heatisnicely linearwithtemperature, following theequation, Specific heat=0.453+(0.155(°C) x10-3) Thethermal conductivity ofbis(2-octyldodecyl)cyclopentane at30°Cis0.165W/(m)(°K), verynearlythe sameasthatoftris(2-octyldodecyl)cyclopentane, andabouttwicethatofperfluoropolyether. Thethermal conductivity ofbis(2-octyldodecyl)cyclopentane at100°Cis0.144W/(m)(°K), Optical Properties Theinfrared spectrum ofbis(2-octyldodecyl) cyclopentane istypicalofasaturated hydrocarbon (Figure 1).Itiscolorless inthevisibleregionandvirtually transparent downto300nmintheultraviolet region. NASA/CP--2002-211506 332
100 o ._ E50 p0 4000; (b) .e_(a) 2700 1800 1000 600 Wavenumbers Figure 1.Infrared Spectra of(a)bis(2-octyldodecyl)cyclopentane, and(b)perfluoropolyether Tribological Properties Vacuum FourBallTribometer Figure 2shows atribometer developed atNASAGlennResearch Center baseduponafour-ball configuration. Itisdesigned totesttheabilityofliquidlubricants toreduce wearunderpuresliding conditions atroomtemperature underavacuum ofatleast106Torr.Thesystem consists ofarotating ballslidingagainst threestationary ballsthatareimmersed inalubricant. Thesystem isloadedthough a pneumatic cylinder, whichpushes thelubricant cupandstationary ballsagainst therotating ball.The lubricant cupisheldinposition byaflexpivot. ! '_Rotating Lubricant _Ball Cup--,. _'/-Stationary  Balls F,exPivot-. Figure2.Detailoffour-ball apparatus NASA/CP--2002-211506 333
Typicaltestsarerunwith9.82mm(3/8in)diameterballs,100RPM,roomtemperature, andaninitial Hertzianstressof3.5GPa.Thisstressdropsasafunctionoftesttimeasawearscardevelopsonthe stationaryballs.Thetestisstoppedeveryhourandthewearscardiametersmeasured. Aspecial platformallowsforthemeasurement ofthewearscarswithoutremovingthemfromthecup[Masukoet al.,1994].Thisallowsthetesttoresumeexactlywhereitwasstopped.Afulltesttakes4hours.Upon completion, thewearvolumeisplottedasafunctionofslidingdistanceandthewearrateiscalculated fromtheslopeoftheline.Thisrigprovidesquickinformation aboutthewearcharacteristics oflubricants andadditivepackagestoreducemetallicwear. SpiralOrbitTribometer Thespiralorbittribometer (SOT),firstintroduced byKingsbury [1989], isessentially athrustbearing with flatraces(plates) andasingleball(Figure 3).Thetribometer simulates rolling,pivoting, andslidingas seeninanactualangular contact bearing. Accelerated testsareachieved byonlyusingmicrogram quantities oflubricant ontheball.Duringthetest,thelubricant iscompletely consumed bytribochemical attack,resulting inshorttestdurations. Theadvantage ofthistypeofacceleration isthatoperational test parameters, suchascontact stress,speed, andtemperature canmimicthoseintheactualapplication. Longlubricated lifetimes implylowlubricant consumption orlowtribochemical degradation rates. Figure3.TheSpiralOrbitTribometer Thetribological elements ofthesystem appear inmoredetailinFigure4.Thelowerplateisstationary whilethetopplatecanrotateatspeeds upto-200RPM.Thetopplaterotation drivestheballinaspiral orbit.Duringeveryorbit,theballcontacts thevertical guideplate,whichreturns theballtotheoriginal orbitradius.Thestraight-line regionwheretheballcontacts theguideplateisdenoted asthe"scrub". The forcetheballexertsontheguideplateduringthescrubismeasured andthecoefficient offrictioncanbe calculated. Afterleaving thescrub,thebali'sspiralorbitbeginsagain.Thespiralorbitandscrubconstitute atrackthatisstable,repeatable, andistraversed thousands oftimesbytheball.Adetailed description of thetribometer andanalysis ofballkinematics appear inReferences byKingsbury, 1989andJonesetal., 2000. NASA/C P--2002-211506 334
/--Ballslideson"Scrub"--3 / Force I/ /topplate transducer _ Guide I/1/ /// \plate--_ I/ / \ \I/ / Orbit\ SpiraltrackI'_'_',/':\'__'__"_"'__-__'- Bottom plate---I--"-"/ "_.-__ Figure4.DetailoftheSOT g2.0E-09 -I 1.5E-09 • 1.0E-09 5.0E-10 0.0E+00IzI X-1000I-Iiz, MAC2001A MAC2001IL__ PFPE143ACPFPEZ25 Figure5.Four-Ball WearRatesforSeveral Lubricants NASA/CP--2002-211506 335
Table1-Comparative properties ofPennzane® SHFX-1000, Pennzane® SHFX-2000, andPFPAE Bis(2octyldodecyl)- cyclopentane (X1000)Tris(2octyldodecyl)- cyclopentane (X-2000)PFPAE(_) 815Z Specific Gravity 0.85 0.85 1.85 Pourpoint(°C) -52 -45 -72 Refractive Index(20°C) VaporPressure 125°C(Torr) 40°C(Torr) Vacuum Outgassing (125°C, 24 hr,10.5Torr) TotalWt.Loss(%) Condensables (%) FlashPoint(°C) Viscosity 100°C(mm2/sec) 40°C(mmZ/sec) -20°C(mPa.sec) -30°C(mPa.sec) -40°c(mPa*sec) Viscosity Index Autoignition Temp (ASTM E659) Hot-flame (AIT) Cool-flame (CFT) Reaction threshold temp1.4682 6x10-_ <0.4% 0.2% 290 9.4 60 3000 8OOO 29,000 131 750°F 610°F 485°F 0.165 0.144Thermal Conductivity1.4671 1.294 4x10-/ 8x10-_ 1x10-1;' 3x10lz <0.2% <0.1% 315 15.0 110 62OO 80,000 135 W/(m)(°K) @30°C W/(m)(°K) @100°C Specific Heat(cal/gm)0.16None 45@99°C 148@38°C 1900 6500(mm2/sec) 35O 0.08 @30°C 0.458 0.52 0.20 @100°C 0.469 (a)DatafromCastrol Industrial NorthAmerica, Downers Grove,IL Results Vacuum FourBallTribometer Thewearrateobtained withtheunformulated X-1000 fluidappears inFigure5alongwithreference data forunformulated andformulated X-2000, aswellastwocommonly usedunformulated perfluoropolyalkylethers (Krytox 143AC andFomblin Z-25).TheZ-25ischemically identical toBrayco 815Z.TheX-1000 hasasimilarwearratecompared totheX-2000 andsignificantly lowerthanthetwo perfluoropolyalkylether fluids. SpiralOrbitTribometer Thenormalized lifetime forX-1000 atameanHertzian stressof1.5GPaappears inFigure6.For comparison, resultsobtained previously with440Csteelspecimens [Jonesetal.,2001]areshownfor unformulated andformulated X-2000, Krytox143AC, andBrayco 815ZAscanbeseen,theX-1000 fluid performs betterthantheunformulated X-2000 fluidandiscomparable totheformulated X-2000. In NASA/CP--2002-211506 336
addition,itsnormalized lifetimeistwoordersofmagnitudegreaterthan815Zand30timesgreaterthan Krytox143AC. 10000 =k 1000- *v.._ O ,_,,( *-' 100 N  10-' O X-1000 MAC 2001AMAC 2001 143AC Figure6.Normalizedlifetimes(orbits/_g)from theSOT815Z Conclusion Pennzane ®Synthesized Hydrocarbon FluidX-1000, alowermolecular weightrelative ofPennzane ®SHF X-2000, hastheexpected lowerviscosity andlowerpourpoint.Although thevolatility isgreater, itstill exhibits vacuum outgassing oflessthan0.5%.Inaddition, itperforms equally aswellasX-2000 asa boundary lubricant intribological testing(i.e.,lowmetallic wearratesinpureslidingandlowdegradation ratesinrollingcontact). References Jones,W.R.,Jr.andJansen, M.J.,"Space Tribology", Chapter 31inModern Tribology Handbook, Vol.2, pp1159-1181, CRCPress,BocaRaton,FL(2001) Nguyen, Q.N.,Jones,W.R.,Jr.,"Volatility andWearCharacteristics ofaVariety ofLiquidLubricants for SpaceApplications", Trib.Trans.,44,pp671-677, (2001) Venier, C.G.andCasserly, E.W.,"Multiply-Alkylated Cyclopentanes (MACs): ANewClassofSynthesized Hydrocarbon Fluids", Lubr.Engr.,47,7,pp568-591, (1991) Venier, C.G.,Casserly, E.W.,andGunsel, S.,"Tris(2-octyldodecyl) Cyclopentane, aLowVolatility, Wide LiquidRange, Hydrocarbon Fluid,"J.Syn.Lubr.,9,pp237-252 (1992). NASA/CP--2002-211506 337
Carre,D.G.,Kalogeras,C.G.,Didziulis,S.V.,Fleishauer, P.D.,Bauer,R.,"RecentExperience with SyntheticHydrocarbon LubricantsforSpacecraftApplications", Aerospace ReportTR-95(5935)-3, (1995). Casserly,E.W.,andC.G.Venier(PennzoiI-Quaker State),"Cycloaliphatics", inSynthetic Lubricants and High-Performance Functional FluidsinRudnick, L.R.,andR.L.Shubkin, eds.MarcelDekker, NY (1999). Brown, P.L.,Miller,J.B.,Jones,W.R.,Jr.,Rasmussen, K.,Wheeler, D.R.,Rana,M.,Peri,F.,"TheClouds andtheEarth's Radiant Energy System Elevation Bearing Assembly LifeTest",33rdAerospace Mechanisms Symp., Pasadena, California, NASA/CP-1999-209259, pp197-212, (1999). VanDyk, S.G.,Dietz,B.J.,Street,K.W.,Jones,W.R.,Jr.,Jansen, M.J.,Dube,M.J.,Sharma, R.K.and Predmore, R.E.,"TheRoleofBearing andScarMechanism LifeTesting inFlightQualification ofthe MODIS Instrument", NASATM-2001-210896, April,(2001). Jansen, M.J.,Jones,W.R.,Jr.,Predmore, R.E.,andLoewenthal, S.L.,"Relative Lifetimes ofSeveral SpaceLiquidLubricants UsingaVacuum SpiralOrbitTribometer (SOT)", NASATM2001-210966, June, (2001). Jones,W.R.,Jr.,Poslowski, A.K.,Shogrin, B.A.,Herrera-Fierro, andJansen, M.J.,"Evaluation ofSeveral SpaceLubricants UsingaVacuum Four-Ball Tribometer," Trib.Trans.,42,2,pp.317-323, (1999). Kingsbury, E.,"Tribology inSlowRollingBearings", Mater.Res.Soc.Sym.Proc.,140,437-442, 1989. Jones,W.R.,Jr.,Pepper, S.V.,Jansen, M.J.,Nguyen, Q.N.,Kingsbury, E.P.,Loewenthal, S.,Predmore, R.E.,"ANewApparatus toEvaluate Lubricants forSpaceApplications -TheSpiralOrbitTribometer (SOT)", SAEInt.SpringFuels&Lub.Meet.&Expos., paper2000-01-1828, June(2000). Masuko, M.,Jones,W.,Jansen, R.,Ebihara, B.,Pepper, S.,Helmick, L.,"AVacuum Four-Ball Tribometer toEvaluate LiquidLubricants forSpaceApplications", NASATM-106264, (1994). NASA/C P--2002-211506 338
ISSSGANT GroupLevelOffloading TestMechanism . XilinZhang Abstract TheInternational SpaceStation (ISS)Space-to-Ground Antenna (SGANT) isusedforISScommunication withearththrough theTracking andDataRelaySatellite (TDRSS). Duetothedifferent speeds oftravel between earth,ISSandTDRSS, asteerable SGANT wasrequired ontheISS. Themechanical design ofSGANT isanunbalanced mechanism withinsufficient strength anddriving torquetosupport anddriveitselfina1Genvironment. Forground testing, aspecially designed offloading mechanism isrequired. Basically, thetestmechanism mustoffloadtheSGANT inatwo-axis operation, allowing theSGANT tomovewithinaspecific range,speedandacceleration; therefore theSGANT can movefromelevation 0°to90°andbetestedatboththe0°and90°positions. Theloadintroduced bythe testequipment shouldbelessthan10.17N-m (7.5ft-lbf).Theon-ground groupleveltracking testisquite challenging duetotheunbalanced antenna mechanical designandtoughspecification requirements. Thispaperdescribes thedetailed design, fabrication andcalibration ofthetestmechanism, andhowthe aboverequirements aremet.Theoverallantenna issimplified toamassmodelinordertofacilitate the offloading mechanism designandanalysis. AnactualSGANT massdummy wasmadetocalibrate the system. Thispaperbringstogether thetheoretical analysis andtheindustrial experience thatwererelied upontomeettheabove-mentioned requirements fortheground test.Thelessons learned duringthe calibration phaseareextremely important forfuturedoubleormultiple offloading system designs. TheISS SGANT QMandFMunitspassed theirground testandtheSGANT/Boom fitchecksuccessfully, andthe FlightModel(FM)wasdelivered toSSPFinApril1998.Itisnowinstalled onISSandfunctioning well,as showninFigure1. ;' SGANT Figure1.SGANT Antenna onISS *EMSTechnologies Canada, Ltd.,SpaceandTechnology Group,Ste-Anne-de-Bellevue, Canada Proceedings ofthe36thAerospace Mechanisms Symposium, GlennResearch Center,May15-17,2002 NASA/C P--2002-211506 339
toamassmodelissummarized inFigure2.Information wasbasedontheantenna massreportfromthe CADdesignmodel. Frontsupfo.ce _,,\ oftheRZRS ",, E/'LXe9inbQ _.X \\X% \254nr/(1000") ._  I== / ,/ /232.4nn (9.15" L_ Ls ½ intercon -_'/// .,'1,9ir,bol 15'-'"-''"-",oor-,.y,,35Ibn) RIRI]].34Kg (25Ibr,)--//_liftin9point / //-- totalo.ssyE/IS /.//.,,,,', ,4£,/, d,17,"'',',',it' "'-II!j._iLr-.-"r'q'_[' r'efIpctor ossy - 1,g5k45Ibn)-_.-_ --'9.... . ._. \ ,,,, I",,. \\{,jl[I'--tatolossy.,.vel.qht x_v:,.iItobelifted b./_ _'_,Ificstliftngpont ""_ 46,[8K9(10],81 Ibn) Figure2.Simplification oftheantenna systemtoamassmodel Onecanseethatthemodelincludes allthenecessary massandC/Glocation information relatedto furtherwork.Inthefollowing sections, thismodelwillbefrequently usedfortheoffloading system analysis anddesign. Location ofthebestoffloading points Atheoretical analysis ofthesimplified modelhelpedfindthebalanced offloading point,whichisakeyfor theoveralloffloading systemdesign.Idealoffloading pointsarethosethatcanbalance theoverallsystem inordertoeliminate thetorqueintroduced bytheSGANTweightandtheoffloading systeminboththeEL (elevation) andXEL(Crosselevation) gimbals. Fromdetailed analysis andaseriesofoffloading testsonamassdummy(themassdummydesignis discussed later),itwasfoundthatforatwo-axis gimbaled systemliketheSGANTthebestwaytooffload theoverallsystemwastotheoretically splitthesystemintwo,thenusetwooffloading mechanism systems totakecareofeachportionatthesubsystem balancing point.Thisapproach canreducethe loadonbothgimbalaxes.Inpractice, itwasalsorealizedthatintheSGANT on-ground testconfiguration, themassloadontheELgimbalwillbecarriedbyitsbearings, andthemarginofloadcapacity onthese bearings issufficient tocarrythatload.Therefore, thefollowing calculations takeintoaccount theload introduced bytheoffloading mechanism only,andthemassloadoftheSGANTweightintroduced intothe ELgimbaldrivingmechanism trainisneglected. NASA/CP--2002-211506 341
Thesystem wassplitintofrontandrearsystems, asshowninFigure3.Sincetherearsystem isrelatively simple, aliftingtestfrommassdummy defined itsoffloading point.Thispointwasselected tobeatthe existing MotorDriveAmplifier liftinginterface. Thefinalapplication showsthatthispointisverycloseto therearsystem C/G.Thisiswhy,inbothFigure2andFigure3,thecomponent massandC/Gofthe SGANT rearsystem arenotshown. Should therearsystem bemorecomplicated, thecalculation could bedoneinthesamewayasthatusedtodefinethefrontsystem offloading point. Frorit sur-I:Q/-e c,ftheE'IEl:.: P/'LXeI!-iir"rt-lql .'-)r- i/_ / d2,J4r"lrl,..]N,C)C)""'" -:'_,4r'lr'__!:I15") ,-_ld_ ',._.,._ ELGir-lhc[I........... '..,..., ....,.., 1L4 Ls L_ F]Czo.r"s'y"£,terl intercoN ]45t:(,:l(:I:'IL:,r"l }:'::_=_I,,qir_l-:,l"]. ....:":".Cl',"-,.. ,.. '.. IIF-h,i I, /,,''" ) // RZE!:_:]],]4t:::::,;_,/ j'"J.__ ,/'j, ,,//." //.t.... ,.F" i II II-- Il-:,rl) ,-,_Il-:,rl)_...,..- _,_..._" .,.. ,. ".  Fr-I:-}1f-I_S':/'StE[""1 t irl9Pi-:1ir-it C:l.SS},'I.........ia El L;, L-,, L_ r-'_1:Ipi-tCI'C}'_--.-",/", ...........-......... 15i 9f_--i t:::l.J (.E"4, El tblr"l }) "-- 1:I'2_'I_'I:-I4]:!-:;K!:4"!d':'_' ....."--hondIet,72K93,7L]ILI["1",'1 ....."--t':'tOI ossy,weigh tObclifted b7 firstliftir,9Fi,::_ii-it 46[,''-' II:'lK"'q,.£1-1],:,]ILIrl",,_.. _ , .., Figure3SGANT simplified massmodel SincetheMGSE (Mechanical Ground Support Equipment) interface wassupplied attheRIRSfront surface (another existing liftingpointintheSGANT), thefrontsystem liftingpointwasdefined fromthe RIRSsurface asfollows (refertoFigure3): tl Since___ M=0 M=VY:_¢L WT•LT-I4]•L1-W_°L__ LT _ I Hi_,.-...-W, °L,,=0 NASA/CpI2002-211506 342
Where: WT--TotalMassoftheFrontSubsystem LT-Distance ofthetotalmassC/GtoRIRSfrontsulface Wn-Subassembly Mass Ln-Distance oftheSubassembly massC/GtoRIRSFrontSwface Thecalculation resultsonthefrontsubsystem showsthatthetheoretically balanced liftingpointshouldbe 26mm(1.03")infrontoftheRIRSfrontsurface. Analysis oftheloadintroduced intothegimbals bytheoffloading system Asperspecification requirement No.1,theloadintroduced bytheoffloading mechanism iscalculated as follows. Theinternal friction ofthespringmotoroffloader isomitted fromthefollowing calculation. The worstcasetobeconsidered iswhenboththeELandXELgimbals areatthe5°position. Torque loadintroduced intoELGimbal Inthiscalculation, thesideloadcontribution isthemajorconcern duetothelargedistance between the loading pointandtheELgimbalcenter. RefertoFigure4. TL_l=FLet•D Where: TLe/---Maximum torque loadonELgimbal FL_.t=_•tanoc- --Sideloadffom theoffloadingmechanism D---Distancefrom theliftingpointtoELgimbalcenter tanb. a=tan-l•(D•--_) H---Offloading cablelength a---Worstcaseoffloading cableangle F---Loadonoffloading cable Afterapplying alltheactualdataintotheabove-mentioned formula, themaximum moment is6.24N-m (55.24in-lbf),whichisabout34%lessthanthetargetloadlimit.Thefabrication andmassanalysis report errorisconsidered lessthan10%basedonEMSexperience. Thetotalmargin leftisabout240, therefore, theoffloading geometry arrangement isacceptable. Loadintroduced intotheXEL.qimbal Sincethedistance fromtheloading pointtotheXELgimbalcenteris330.2mm(13")lessthanfortheEL gimbal, thesideloadisnotaconcern intheXELcase.Onlytheacceleration torquerequired fromthe XELgimbalneedstobeconsidered. RefertoFigure5. TLxe,=FLXel•R Where: TLxel---acceleration driving torquerequired fromthe)(elgimbal F,xe,Wl,=--a---acceleration forcerequired g a=a.R a---max.angular acceleration R---liftingpointrotation radius NASA/C P--2002-211506 343
Afterapplyingalltheactualdataintotheaboveequations,themaximumdrivingtorquerequiredisfound tobeonly2.41Ib-in,whichisfarfromthetargetloadlimit,andagainthegeometricarrangement is acceptable. Calculation ofsoftware limits Software limitsarethesecondlayerofsafetydevice,itisusedtoavoidextraloadcausedbyover-travel ofthegimbal.DuringtheSGANTgroupleveltracking test,ifforanyreasonthegimbalsshouldreachthe software limitpoint,thepowerwouldturnofforthedrivingmechanism wouldbedisabled toprotectthe SGANT. Inrequirement 2,thetargetoffloading mechanism designloadislessthan10.17N-m(7.5ft-lbf),which shouldbethenumberusedtodetermine theallowedgimbalover-travel angles.Thecalculation methodis asfollows: Calculation oftheEL.qimbalsoftware limits Withreference toFigure4: ,8S_m=tan-1d/D where: J_Slim ----- Software Stopangle d=H•tana a=tan-1Flirn/W1 Flim---Maximum load(Introduction requirement 2) Elim--Tlim/d W_---Subsystem weight Applying alltheactualdatatotheformula, thecalculated software limitis7.525°.7.5°isthelimitselected. Definition oftheXEL.qimbalsoftware limits Thiscalculation isomittedbecause thetorqueloadintroduced bytheoffloading systemintheXELcaseis relatively small.Thesoftware limitwassetat7.5°tomakeitthesameastheELgirnbal.Itisclearthatthe gimbalwillnotencounter problems withinthatlimit. Mechanical designofthetestsystem Afteralloftheabove-mentioned offloading pointsweredefined, themechanical offloading systemwas designed asfollows. Itincludes amainstructure tosupportthesystemonthecompact antenna range turntable, theconstant forcespringmotoroffloading system,theSGANT transferandinstallation system, thehardmechanical stopsandanelectrical stopsystem. Theoffloading methods arethemaintopic covered inthispaper. Duringbrainstorming sessions, manypossible methods werelistedfortheoffloading test.Thecable pulleyandweightsystemandtheconstant forcespringmotoroffloading systemreceived thehighest tradeoffscoresinallrespects. Figures6and7showthesetwodifferent offloaded testsystemdesigns. NASA/CP--2002-211506 345