ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
generations ofpumphardware developed duringthisPhase11SBIRandIR&Dactivity. Piezoelectric PumpDevelopment PhaseIISBIRPrototype Summary ofDetails Adouble-acting diaphragm pumpdrivenby piezoelectric polymer filmswasdesigned, constructed andtestedaspartofthePhaseII SBIR.Theinitialactuators wereconstructed of piezoelectric polymer filmsthatarelaminated intoeightforty-layer stacks, arranged sothat charging thecomposite structure causes ittomounting blocks Figure2.UnitCell.conductive hinge mechanical hinge flex.Onesuchstackisreferred toasabender (Figure 1)andtwobenders connected byhingesattheir endsarereferred toasaunitcell(Figure 2).Foursuchunitsdrivetheoriginal pump(Figure 3).Anovel electrical circuitdeveloped specifically forthis application (Figure 4)powers thedrive mechanism. Theunitcellsactascapacitors, withonlyasmallfraction oftheenergy inputto thedevicebeingconverted toflowpowerin eachcycle.Thecircuitthatwasdeveloped as partofthisdesignprovides switching which eliminates boththewasteofenergyinherent in direct-drive circuits andtheneedforlarge inductors ortransformers. Figure3:PhaseIIPumpTestsofthepumpshowthatitisabletopump upto61kg/hrofwateratadifferential pressure of7590Pa(1.1psi)or23kg/hrat20000Pa(9 psi).Theseconditions represent approximately 60%ofthedesigngoalsof100kg/hrand32480 Pa(5psi).Theresultswereobtained atinput voltage levelsofupto400V.Thedesign COICTROL SZGN_ I Plezo Film I RI  2Replenish Centrol s'roP_'lg INDUCTOR iTN_C ] --_. U1TRIAC DRIVER 4 1R4 Fiqure4:NovelElectrical DriveCircuit 158
shouldbestableto800Vwhichwouldallowthedesigngoalstobefullyreached. Thevoltagehasbeen limitedintestingtoavoidprematurely damaging theprototype. UNITCnl PISTO,I_I Figure 5a:Schmatic ofPumpx(t)____ k_Ik_R /....._.. --_ Figure 5b:Dynamic Model ofPump DriveBlockAnalysis endSizing[2] Stacksandarraysofunitcellsarereferred toasdriveblocks. Inordertosizethepumpdriveblocks,it wasnecessary tomathematically characterize themotionofthepistonasafunction ofthegeometry of thebenders andthepressure onthefaceofthepiston. Inordertodothis,theschematic layoutofthe pumpshowninFigure5awasreduced toaone-dimensional dynamic systems modelasshowninFigure 5b.Inthisfigurethesprings(k)eachrepresent thestiffness ofonestackofpiezoelectric benders, the mass(M)represents themassofthepistonandplateplustheeffective massofthebenders, the damping (R)relatestoviscouslossesintheLCVG(theloadonthepump),andtheforcegenerators (F) eachrepresent thepiezoelectrically-induced forceofonestackofbenders. Thismodelisofvalue because itprovides closed-form solutions whichindicate thedependence ofthesolution uponvarious parameters. Thesesolutions formthebasisforthedriveelement sizingcalculations. Inaddition, these calculations provideelectrical impedance formulas foruseintheelectrical drivecircuitry development. Theanalysis methodology isdescribed below. Thepiezoelectric forceinaunitcellis F=_le31V, where(1) 3weh2eff OSl- , (2) 2t/L weisthewidthoftheelectrode, heffistheeffective thickness ofabender, tjisthepiezoelectric film thickness, Listhelengthofthebenders, e31isthepiezoelectric stressconstant, andVistheapplied voltage. ThestaticloadPwhichaunitcellcanliftisgivenby P=-kx+ot]e3]V , (3) wherekisthestiffness oftheunitcellandxisthedisplacement ofthetopoftheunitcellwhenthebottom surfaceisfixedinplace. Usingequation 3,thedynamic motionofthepumppistoncanbecomputed usingtheequation ofmotion givenby MR+IL_:+4kx--4ot,e,,V (4) 159
wherethefactorof4representsthe4unitcellsusedinthedesign.Givenasinusoidalvoltageinputwith afrequency_thepistonwilloscillatewithanamplitudeXgivenby I X=atle31V° 1 (5) k'.J (oR l2 +7.) v whereV0isthemagnitude ofthevoltagesignal,[e3,[isthemagnitude ofthecomplex piezoelectric stress constant, k'istherealcomponent ofthestiffness, Qmisthemechanical qualityoftheunitcells,andr= el'_istheratiooftheimposed frequency cotothenaturalfrequency ofthesystem(_givenby co=V_r: (6)i Theflowratewhichthepumpcandriveisthencomputed as (.o (7) Q=4XAp"°" 2zr' whereApi,to,,istheareaofthepistonface.Thefactorof4inequation 7occursbecause thetotalstrokeof thepistonistwicetheamplitude andtherearetwopumpheads. Thecurrentdensityiinapiezoelectric filmlayeriscomputed usingtherelation OSll 1dV i=e3l---_ +-E33tidt'(8) where$1_istheaverage straininthepiezoelectric filmatthepointinquestion andE33isthepermittivity of thefilm.Integrating equation 8overtheentirecomposite structure ofabenderandtotalingthe8benders inaunitcellgivesanequation oftheform I=[(G(o_)+ oK7'tanS)+j(B(oJ)+ o.,'C')]V, (9) whereV=I'1oe:_'isthevoltagesignal, C-8(2N)weLe;3 (10) tf istherealpartofthecapacitance ofaunitcellwith2Nequaltothenumberoffilmlayersineachbender, thefactorof8represents the8benders whichmakeupthe4unitcells,tan8isthedielectric losstangent, • 2#2 Qe3, Oe3, Qm <1 G(co)=4foaie3i Jt&+ + + (11) k" (l_r2)2+_7+Q-_m(OR 3(1_.+--_-)Qm) • 2,2 B(co)- 40_,e3_ k" andQ<_istheratiooftherealtothe(1_.___12 _l_r2)_ 2((.0/_+ ')(-A-i-I)21t Qe,,) \ -_e3tt --_-_ -_mf 1--Qe3, Oe3, Pm (,Iimaginary partsofe_.(12) 160
Theelectricalpowerinputtothesystemisgivenby ='Vo2(G((O)+ (.oC'tan 6) andthepoweroutputbythepumpisgivenby aj2(.O2[e312 Rz02 (oR!),(I-r2)2+(_-7+Q,,(13) (14) Therefore thebasicefficiency ofthepumpcanbecomputed as 22 Pouta12(-0e31 R l 11-.p.-k,2 (oR 12G((o)+ (_oC'tan_" (15) 0-r )+(yE+ Theaboveequations areusedtosizethepump.Thecriticalequations are6,7,and15.Fromequation 5itcanbeseenthatthemaximum displacement canbeobtained ifthepumpisrunatresonance (r=l). Thisistruesolongastheo_R/4k'is nottoolarge.Largevaluesoftheviscousresistance Roverdamp the systemanddonotallowresonance tooccur.However, ifthepumpusesaccumulators sothatthepiston isworking againstconstant pressure, resonance canalwaysbeobtained. Inthiscasethepointof resonance alsogivesthemaximum efficiency. Figure6:Second Prototype Developed UnderIR&D SecondPro.totype Developed Un_lerIR&D OSScontinued thepumpdesignwithanew-generation modelbuiltunderIR&Dfunding. Themajorgoals ofthisworkweretoreducetheoperating voltage(fromthe800Vfirstmodel),andtoreducethevolume whileimproving efficiency. Thefollow-on work,basedontheresultsdeveloped aspartofthe aforementioned prototype, wasrecently completed. Theworkdemonstrates designoptimizations that allowanorder-of-magnitude reduction inrequired operating voltages (toapproximately 40V)while retaining appropriately highfieldstrengths withintheactivepiezoelectric material. Additional workhas alsobeencompleted thatdemonstrates amaterial substitution basedonhybridpiezo-thermoplastic 2-2 composites. Thissubstitution hasresulted inanorder-of-magnitude reduction inthetotalvolume required foragivenunitofusefulworkoutput,withsignificantly improved efficiency (ontheorderof65%) 161
withrespecttothePhaseIIpolymerdesigns.Additionaldesignimprovements beinginvestigated include hingeimprovements, metalbellows, andvibration elimination. Thesecondprototype wascapableofproducing halfoftheflowandforceofthefirstprototype atonethirtieththevolumeandone-fourth thedrivevoltage. Wearecurrently seekingfundingtocomplete the process ofcharacterization andtodevelop mathematical modelsforthenewhybridgeometry. The preliminary resultsarepromising. Fourpatentshavebeenissuedcovering thefabrication ofthebenders [3],theunitcellgeometry [4], application ofthepiezoelectric unitcellstopumpdesign[5],andtheelectrical circuit[6].Additional patentsbasedonthemostrecentworkwithlow-voltage hybridpiezo-thermoplastic composites werefiled lastsummer. Inaddition tothedirectapplication ofpiezoelectric pumpstoactivethermalcoolingforlifesupport applications, converse-piezoelectric pumpsoffergreatpotential inthedual-use areaofalternative electromechanical actuators. Asanactuator, thispumpmayprovidesolutions tocontrolsystemproblems in robotics, processcontrol,bioengineering, andadvanced remotecontrol(telepresence) technologies. The advancement ofthesetechnologies iscoupled toimprovement incontrolsystemengineering whichisa centralengineering problem. SomeSpaceAPPlications •High-reliability low-power pumpsforfluidmanagement duringplanetary missions •Circulation pumpforfluidsinwaterstoragesystemtopreventbacteria growthonwalls •General actuator foravarietyofspaceapplications including automation androboticimplementations •Activethermalcontrolforspacecraft •Activethermalwaterloopsforspacerefrigeration systems •Primaryflowcontrolforspace-based biological reactors •Metering pumpstocontrolspace-based pharmaceutical production processes Conclusion Piezoelectrically-driven pumptechnology promises reduced mechanical complexity, increased reliability, improved efficiency, reduced volume, andreduced weight,withrespecttoconventional pumps. This paperdescribes characterization equations, analysis, andworkinghardware thatillustrate thesepossible improvements. Thehardware iscurrently approaching alevelpractical foruseinspacetoday.A concerted effortshouldbemadetoadvance piezoelectrically drivenpumps. References 1.Piezoelectric WaterPumpforUseinExtraVehicular Activities PhaseIFinalReportNAS9-18850. 2.ExcerptfromPiezoelectric WaterPumpforuseinExtravehicular Activities phase11finalreport(NAS 9-19104). Theoriginalanalysis wasperformed byChristopher J.MaticePh.D.,PEwithStress Engineering Services, Inc. 3.U.S.Patent#5,761,782 forMethodofFabrication ofBenders, issued06/09/98. 4.U.S.Patent#5,889,354 forUnitCellGeometry, issued03/30/99. 5.U.S.Patent#5,798,600 forApplication ofPiezoelectric UnitCellstoPumpDesign,issued08/25/98. 6.U.S.Patent#5,892,314 forElectrical DriveCircuit,issued04/06/99. 162
Miniature LinearActuator Armond Asadurian" Abstract Theobjective wastodesignanddevelop alinearactuator fortwodifferent applications usingonebasic designphilosophy. Thebasicdesignconfiguration wasbasedonanincremental rotaryactuator, which wasderived fromthefamilyofstandard SMDactuators. Linearmotionwasobtained fromaprecision ballscrew attached totherotaryoutputmember oftheactuator. Thisarrangement produced alinear outputmotionatthematingball-nut. Inoneapplication, theactuator wasusedtoprecisely position two slidingloadswithinaRFVariable PowerDivider. Theotherapplication required thelinearactuator to rotateareflector aroundagimbalpivotpointwithinanAntenna Pointing Mechanism. Design Challenges Theprincipal designchallenges werethecompact andlightweightarrangement, therequired accuracy, andtherequirement toproduce relatively largelinearforceswithinthetemperature andsizelimitations. Theseperformance demands weremagnified bytheadditional requirements ofmeeting 2:1torque margins withinthespecified powerconsumption requirements, redundant motorwindings, redundant fine (rotary) andcoarse(linear) potentiometers usedfortelemetry, redundant heaters, thermistors, and thermostats. Introduction andProduct Description Thisdesignutilizesastepper motor,whichfurnishes theinputtoaharmonic drivespeedreducer. The ballscrew isattached totheoutputoftheharmonic driveandissupported withaduplexpairofangular contact ballbearings (Figure 1).Atwo-track (redundant) rotarypotentiometer ismounted ontheoutputof theharmonic drive,andishoused aroundtherotating axisoftheballscrew, occupying onlyasmallaxial space. Figure1.LinearActuator (50-mm stroke) *Moog,Inc.,Schaeffer Magnetics Division, Chatsworth, CA th Proceedings ofthe34Aerospace Mechanisms Symposium, Goddard SpaceFlightCenter,May10-12,2000 163
actuator,andthelinearpotentiometer wasconnectedtothenutoftheballscrewassembly. Combining therotaryandlinearactuatorresultedinasystemaccuracy/resolution of23.6tJm(0.00093inch). Actuator Performance Characteristics Winding resistance (ohms) Inductance (mH) RotaryPotentiometer Resistance (ohms) LinearPotentiometer Resistance (ohms) PowerConsumption (watts) Threshold Voltage, Hot(V) Threshold Voltage, Cold(V) Potentiometer Linearity LinearStepSize(IJm) Repeatability (pm) Ballscrew Backlash (IJm) System Accuracy over5-cmstroke(tJm) Stroke(cm) Operating Temperature (°C) Mass(kg) Actuation Forcerequirement (N) Actuation Speed{(PPS)PulsePerSecond}50.5 15 9255-10544 7077-7428 15.44 10.0 17.0 (SeeFigure3asanexample) 1.75(0.000069 in) +20(+0.0008) 7.6(0.0003 in) +25(+0.001 in) 5and0.65(1.9685 and0.2559 in) -50°Cto+85°C 0.5max.(1.10lb) 93(21Ib) 3OO Lessons Learned B_lls(;:rew vs.Leadscrew Theinitialdesignapproach wasbasedonaleadscrew (plainscrew)withaVespel material nut.This approach wasconsidered inordertoeliminate theneedforalubricated leadscrew. TheVespel material nutwasselected foritsself-lubricating characteristics andspaceenvironment qualification. Theinitial resultsdemonstrated anutandscrewcombination thatwasefficient enough tomeetthedrivingforce requirement without theuseoflubricant yetresisted thebackdriving oftheoverallsystem duetothe payload reaction forces. Theotheradvantages werelightweight, andasimpleandcosteffective mechanism. Themechanism wasthenanalyzed foraccuracy andthermal characteristics. Thechallenge wasto designtheVespel nutwithaspecific threadshapetomitigate theeffectofthethermal coefficient differences between theVespel material andthestainless steelleadscrew. Duetothelargetemperature spanandthetightaccuracy requirement ofthesystem, theuseoftheVespel nutincombination withthe stainless steelleadscrew wasrejected forthisactuator. Thecombination ofthesetwodissimilar materials canbeaviableoptionintheeventthatthepayload canbeconstantly springloadedinonedirection producing unidirectional loading ofthenutandeliminating backlash underallconditions. Current limitedsystem vs.V01taqe drivensystem Theelectronic interface specified avoltage drivensystem thatwasvoltage regulated, withthevoltage set ataspecified limitandthecurrentdrawthendepending onthewinding resistance ofthemotor. This resulted inpowerconsumption exceeding therequirement atcoldtemperatures. Bylimiting thecurrent drawtoaleveladequate forproducing therequired torque, wewereabletoprevent excessive power consumption atlowertemperatures. Anti-Rotation Member Thetendency oftheball-nut torotateduetothetorqueatthescrewwascountered byananti-rotation bar extending alongthescrewaxisandproviding support fortheball-nut. Thealignment ofthisanti-rotation bartotheaxisofthescrewisimportant. Anymisalignment willcausearotation oftheball-nut asit movesfromoneendoftheballscrew totheotherend.Thisslightrotation ofthenutwillcontribute tothe 165
accuracybudgetoftheoverallactuator.Thisconditionwillalsoapplytoasysteminwhichthepayloadis notaccuratelyguided,allowingrotationoftheball-nut.Thisrotationmustbeidentifiedandaccountedfor duringthedesignanddevelopment phase. Evaluation Testing Anextensive qualification testingprogram wasperformed forthislinearactuator. Testing wascomprised oftopassembly leveltestingaswellasdetailcomponent testing. Thedetailcomponent testswere performed ontheharmonic drive,ballscrew, motor,andpotentiometer assemblies. Thetoplevel assembly testingconsisted offunctional, vibration andthermal vacuum testing. Thefunctional testingwascomprised ofpotentiometer linearity, outputforce,stepsizerepeatability, and backlash tests.Thesefunctional testswererepeated aftervibration andthermal vacuum testing. Results indicated thatactuator performance wasnotdegraded duetoexposure tovibration andenvironmental conditions. .....-..... __ ,_._-_o-'_-.,_,N_,, _,,,._,_:_-,_- _ Figure2.LinearActuator Cross-section I Linearity -PriFineRun3(extend) J c1stn002:min&maxvaluesbelowleft(Spec:FinePot+/-.5%,CoarsePot+/-2%) 0.60% 0.40% 0.20% "t0.00% -0.20% -0.40% -0.60%\ iiiJiii-i--JiI-['lIt__JIIIIJI 64 704 1344 StepsTravelled I--para. 3.3.5--min-.5%--max+.5% J Figure3.ASample Actuator Linearity TestPlot 166
TheSandmeier FieldGoniometer: AMeasurement ToolforBi-directional Reflectance MarkTurner* andJeffBrown Abstract Recentactivities attheRemote Sensing Program atStennis SpaceCenterhaveidentified theneedto properly verifyandvalidate dataprovided bytheremotesensing community. Oneimportant variable, whicheffectsremote sensing dataisbi-directional reflectance distribution (BRDF). Inordertoquantify theeffectsofBRDFonman-made andnaturalgroundtargets, theStennis Verification &Validation (V&V) teamcommissioned theSystems Engineering Division atNASAAmesResearch Centertodevelop a FieldGoniometer foruseattheV&VLargeTargetRangeandforvarious ground truthing missions. TheSwissFieldGoniometer (FIGOS) wasusedasabenchmark instrument todesignthenewstateofthe artSandmeier FieldGoniometer (SGF),namedafterStefanSandmeier, developer ofFIGOS. After establishing requirements fortheSFG,designeffortsbeganinearlyMay1998.ThedesignoftheSFG wascompleted inSeptember 1998.Manufacturing, construction, andtestingwascompleted inMay 1999.TheSFGwasshipped toNASASSCandfullyoperational byJune1999. Introduction Depending ontheviewing angleofthesensor(satellite oraircraft) relative tothetarget(vegetation or geology) andirradiance source(sun),theintensity ofreflected radiance fromthetargetcanvary considerably. Thisphenomenon isknownasbi-directional reflectance distribution. Inaddition toBRDF beingcaused bythevariable position ofthesunrelative tothetarget,seasonal effectssuchasrainand snowcaneffecttheBRDF. BRDFcanalsobeattributed tovarying viewing geometry caused whenan instrument's fieldofviewislarge. tnremote sensing applications, BRDFcanalterthespectral signature ofthetargetthuslimiting the usefulness ofremote sensing data.Byquantifying BRDF,theusefulness ofremote sensing datamaybe improved. Tomeasure theeffectsofBRDFonvarious targets, aFieldGoniometer isused.UsingaField Goniometer, BRDFcharacterization ofspecific man-made andnaturaltargetscanbeaccomplished. In addition, adatabase ofbi-directional reflectance signatures inthevisibleandnearIRcanbecreated for various targets. Figure1illustrates thegeneral principle ofmeasuring BRDFusingaGoniometer. Lightsource (Sun)__ TZenithal arc _,_radiometer _al arc I= 4m -i Figure 1Measurement ofBRDFusingaFieldGoniometer *NASAAmesResearch Center, Mountain View,CA Proceedings ofthe34"_Aerospace Mechanisms Symposium, Goddard SpaceFlightCenter,May10-12,2000 167
Sandmeier FieldGoniometer Background Tosupport V&VeffortsoftheRemote Sensing Program atStennis SpaceCenter, theneedforaField Goniometer forquantifying BRDFwasidentified. TheStennis V&Vteamcommissioned theSystems Engineering Division atNASAAmesResearch Centertodevelop aFieldGoniometer foruseatthe Stennis SpaceCenterV&VLargeTargetRange. TheSwissFieldGoniometer (FIGOS) wasidentified as thebenchmark instrument forBRDFmeasurement inthefield.V&Vteammembers addednew requirements tocustomize theinstrument fortheirparticular needsandtoincorporate lessons learned duringtheoperation oftheoriginal instrument. Figure2illustrates thesolidmodeldesignofthe Sandmeier FieldGoniometer. TheactualSandmeier FieldGoniometer isshowninFigure3undergoing acceptance testingatStennis SpaceCenter. Figure 2.Sandmeier FieldGoniometer Requirements Development Toensureconsistency withdataobtained fromFIGOS, thenewFieldGoniometer maintains thesame pathoftravelfortheSpectroradiometer, theinstrument thatmeasures irradiance inthevisibleandinfraredspectrum. The3degreefieldofviewand2meterdistance fromtheinstrument tothetargethasalso beenmaintained. Thefollowing arethekeyperformance requirements oftheSFG: •TheSFGshallbecapable ofproviding measurements ofthewavelength dependent reflected electromagnetic energyfromatargetonthegroundinthewavelength rangeof400-2500nmwitha constant distance between thesensorandthetargetof2meters. •Thecapability shallbeprovided tomeasure atotalof66sample locations, (11samples perzenith arcat6azimuth locations) innomorethan15minutes withatargetgoalof8minutes (TheSFG shouldmakethesamestandard sixty-six measurements astheFIGOSinordertocompare measurements madebythetwosystems) •Thecapability shallbeprovided toautomatically sample atzenithanglesfrom-75degrees to+75 degrees in15degree intervals andazimuth anglesfrom0-180degrees in30degree intervals •TheSFGshallhaveapointing accuracy through allzenith(-75degrees to+75degrees) andall azimuth angles(0-360degrees) oflessthan+/-3.5cminanydirection, asmeasured byalaserspot onthegroundtarget,whichrepresents thecenterofthespectroradiometer fieldofview(FOV). •Whenthespectroradiometer isatnadir,itsFOVofthegroundtargetwillbe10.5cmdiameter orless. 168
•TheSFGstructureshallnotshadowthetargetwhenmeasuringinthesolarprincipalplane,(azimuth ofspectroradiometer alignedwithazimuthofthesun).Thespectroradiometer sensorheadwillbe designed,totheextentpossible,toreducetheamountofshadowingonthetarget. •TheSFGshallbedesignedoperateonterrainwithslopesofupto10%grade. •TheSFGshallhaverepeatableperformance throughout disassembly andreassembly in environments witharangeoftemperatures between-2degCand38degCwitharangeofrelative humidityof10%-95% Additionalfunctionalandoperational requirements wereaddedwhichallowtheSFGtobeusedon repeatedcharacterization, whichprovideassuredrepeatability indatacollection. Figure3.TheSandmeier FieldGoniometer atStennis SpaceCenter Figure 4.Spectroradiometer mounted onInstrument Sled 169
Design Description TheSFGusesanoff-the-shelf GER3700spectroradiometer capable oftakingmeasurements inthe wavelength rangeof400-2500nm.Acustom Fore-optic lensismounted tothespectroradiometer to decrease shadowing effectsthatwouldoccuriftheinstrument wereplaceddirectly overthetargetpath. Theinstrument sled,showninFigure4,supports theGER3700andfore-optic lensandincorporates an alignment platetoallowforfine-tuning oftheinstrument's opticalpathrelative tothetargetoncethe Goniometer isfullyassembled. Structural Desian TheZenithArcAssembly isdesigned tobedisassembled intotwohalvestofacilitate transport. Sincethe SFGwillbedeployed inremote locations, emphasis wasplacedonreducing weighttotheextent practical. Theentirestructure isfabricated outof6061-T6 aluminum andeachhalfarcweighs 14.5kg (32Ib).Tomaintain atargetpointing accuracy of+3.5cm,therollingsurface ofthezenitharcmustbe radially concentric towithin3mmoverthedistance spanned bytherollersontheInstrument Sled.To achieve thisprecision, theupperrollingsurface wasmachine screwfastened toawelded support structure. Thisallowed theuseofshimstocktobeaddedtocompensate foranywarpage experienced whenthestructural framewaswelded. Thedecision toweldthemainstructure wasmadetoreducethe fabrication cost,sincemultiple unitswereplanned. Guidepinslocated attheupward matingsurface allowforprecise repeatable alignment (Figure 5).Captive fasteners areprovided forallmatinglocations. Figure 5.ZenithArcMating Surfaces Adesigntrademadewithrespect tothestructural assembly wastoconsider suspending theinstrument fromthetrussandinvertthetrussfromitscurrent orientation. Thisapproach wasruledoutbecause it wouldhavecomplicated thebeltdrivedesign. Thecurrentdesignallowsforthedrivebelttobetensioned overthetopoftheofthezenithframe. Theuseofanall-composite zenithframewithtriangular cross section wasconsidered butwasruledoutduetohighermanufacturing costandconcerns about shrinkage andwarpage totheframe. Therewasmuchconsideration giventofabrication methods used toconstruct aprecision welded structure. Theconcern wasthatanintricate thinwallaluminum structure wouldexperience fartoomuchwarpage tobeconsidered asadesignchoice. Byusinglowamperage Tungsten InertWelding (TIG),andpropersequencing ofthewelds, thezenithstructure wasfabricated withnomeasurable distortions inanyaxis.Noshimswererequired inthefinalassembly. 170