ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
andfixturingoncetheycouldseethehardwareandtrulyunderstand theintent.Thezero-gravity docking testwaspostponedadaypendingresolutionoftheseissues.TheReviewBoard'smainconcerninvolved thelowprobabilityofreturningaheavyfreefloatingmass(>113kg(250Ib))toafixturecradlepriortothe 2-gpartoftheparaboliccycle.Thesolutionwastomodifythefixturesbysimplifying themandby reducingtheirweightto<45kg(<100Ib).Intheend,alltestswererunfromtheflooroftheaircraftwhere averysimplifiedfixturesupportwascreatedofpadded2x4sandplywood. Theexperiment wasdesignedtohavetwoseparatefreefloatingsimulatorsrepresenting therelative inertiaofaclientandservicingsatellite(approximately a2/1ratioclienttoservicing)(Figure7).Eachhalf oftheMDSinterfacewasmountedtoaseparateinertia/mass simulator.Duringthemicro-gravity phase thehardwareandrelatedmass/inertia simulatorsfloatedupaboveastationaryfixturecradle.WithJSC crewassistance, thetwohalveswerepositionedwithincapturerange.Theactivedockingmechanism wasimmediately poweredinanattempttodemonstrate "zero"gravitydocking.Becauseofthelimited timeinmicro-gravity, consecutive phasesofthedockingsequencewereperformedthroughout aseriesof parabolas. ItisimportanttonoteherethattheJSCcrew'sassistance wasinvaluableinexecutingthe plannedtests.Notonlyweretheyavailabletoassistinrunningthetestsshouldteammembersbecomeill (motionsickness),theirextensiveexperience workinginamicro-gravity environment madethevery difficulttaskspossible. Thesemicro-gravity testsdemonstrated twoprimarypoints.First,itwasclearthatthedesignhad sufficientcompliance inthelinkagestopreventa"rebound"effect.Therewereconcernsearlyonthatthe relativelysmallimpactforcesassociated withdockingin"zero"gravitywouldcausethespacecraft to moveoutofcapturerangeastheyreactedagainstoneanotherduringthedockingphase.Thisprovedto beoflittleconcernduringtest,butitdidemphasize theimportance forcompliantlinkages.Second,there aredefinitelimitationstotestingfree-floating dockingmechanisms ontheKC-135.AlthoughtheMDSwas consistently successful incapturingthepassivesidewhenthecapturerangewaswithinspecified guidelines, certainspecificattemptstocapturefailed.Thisresultedfromeitherthecapturerangebeing toolarge(i.e.,conditionsdidnotallowproperpositioning oftheinterfaces) orthefree-floating inertia impactedthesidesorflooroftheaircraft.Thesetwoeventsoccurredbecauseofinherentdifficulties workingandstabilizinginamicro-gravity environment orbecauseofexperiment "drift"resultingfrom unfavorable flightpatterns.Actual"zero"gravitytimewasreducedsignificantly whenthetestcrewhadto adjustandlimittraveloftheexperiment asaresultoftheseconditions. Figure7.Micro-Gravity Testing ofMDSonNASA's KC-135 ("Vomit Comet") Computer Simulation: Thefinalphaseoftestinginvolved performing stiffness testsontheprototype hardware. Lateralandradial stiffness wasmeasured inboththedeployed andcaptured position ofthelinkage assemblies. By NASA/CP--2002-211506 275
includingthesemeasuredstiffnessvaluesnthedynamicsimulationmodel,morepreciseresultswere possible.Resultsofthestiffnessmeasurements arepresentedinTable3. Table3.Linkage Stiffness TestResults Configuration Compliance cm(in) Deployed Radial 0.23-0.33 (0.09-0.13) Lateral 0.67-0.95 (0.265-0.375) Captured Radial NoData Lateral 0.46-0.62 (0.18-0.245)Stiffness N/cm(Ib/in) 140-147 (80-84) 70-74(40-42) 114-145 (65-83) 58-63(33-36) Dynamic Analysis andDesign System (DADDS) software wasusedtomodelthecapture andretraction features oftheMDS3.Themodelincluded massproperties oftwosatellites, zerogravity, andcontacting features oftheMDS(i.e.,ballendsoflinkage assemblies). Themodelaccurately simulated the kinematics ofthefour-bar linkages, including dynamic reaction loadsatallpointsofinterest. Somehand-selected caseswithsimpleworstcaserelative misalignments weresimulated andexamined, withthefocusonidentifying general issuesofconcern. Examination oftheresultsoftheseanalyses revealed thefollowing issues: a)alikelihood ofhighloadsatcertainMDSlocations b)possible difficulty in axialrollalignment duringretraction c)possible difficulty intimelyremoval ofpitch/yaw misalignments. Anadditional 400casesweresimulated toexplore performance issuesusingauniform distribution of initialcondition parameters. Theanalysis concluded thattheMDSalways positively captures thepassive sidegivenreasonable limitsoninitialtestconditions. Acasewithcombined misalignments demonstrating highloads(Case1),acasewithpurerollmisalignment of5degrees andaxialoffsetof9cm(nodata provided) (Case2),andacaseofslowpitch/yaw angleremoval (Case3)arerepresented inTable4and Figure8. Table4.Simulation TestConditions HighLoad(Case1) InitialConditions TestCaseBounds Relative position Relative linearrate Relative angular position Relative angular rate SlowPitch/Yaw Angle Removal (Case3) Relative position Relative linearrate Relative angular position Relative angular ratex=3.0cm,y=-2.1cm,z=6.4cm xd=0.164,yd=-0.074,zd=-0.159 ax=-2.6, ay=-2.2,az=-1.5 wx=0.064,wy=-0.080, wz=-0.097 InitialConditions x=2.8cm,y=2.9cm,z=8.2cm xd=-0.215, yd=-0.054, zd=-0.152 ax=-3.5,ay=3.6,az=-3.8 wx=0.085,wy=-0.022, wz=-0.090(-5<x,y<5cm),(5<z<9cm) -0.25<xd,yd,zd <0.25cm/s) (-4<ax,ay,az<4deg) (-0.1<wx,wy,wz<0.1deq/s) TestCaseBounds (-5<x,y< 5cm),(5<z<9cm) (-0.25<xd,yd,zd <0.25cm/s) (-4<ax,ay,az<4deq) (-0.1<wx,wy,wz<0.1deg/s) 3TheBoeing SpaceandDefense Groupgreatlysupported SRCandthedevelopment effortby performing thesedynamic simulations. NASA/CP--2002-211506 276
Case1 Case2 Case3 Figure8.Misalignment Cases Lessons Learned Anevaluation ofthedesignanddevelopment process hasprovided insightintoaspects oftheprocess as wellasintopotential designimprovements. Don't"Reinvent theWheel": Theprocess ofthoroughly reviewing allexisting hardware, trading these against requirements, performing atrulyunbiased tradestudy,andthendesigning fromtheoutput proved invaluable. Theresultwasoptimum andhasbeenvalidated through theselection oftheMDS byanOrbitalExpress team. Don'tforcenewtechnoloqies wheretheyaren'tneeded: Applying newratherthanexisting technology isnotalways preferred. Thetechnical riskandlimitations ofadvanced technologies often tradepoorlyagainst existing proven approaches. Thechoicetoswitchtoatraditional motordriven coupling system, inhindsight, wascriticaltothesuccess ofthesystem. Nitinolwouldhaveworked; theresulting devicewouldhavebeenclever,innovative, butfunctionally limited. A"requirements vacuum" canbeapowerful environment forforwardinq technology: Itallowsthe designer tolookaheadandderiverequirements tomeetfutureneeds. Itenables "products" tobe developed thathaveutilityforavariety ofusers.But,undertheseconditions, theteammustavoid tendencies tosimplydesign, without vision. Utilizincl avarietyoftestmethods tovalidate adesiqncanbevaluable: Whendesigning tooperate outside gravity buttesting under theinfluence ofgravity, finding anappropriate testmethod iscritical todesignvalidation. Thethreemethods applied (off-loading, micro-gravity, andcomputer simulations) allcontributed toanoverallunderstanding oftheMDS.However, theapplication ofahighlyreliable computer simulation modelproved invaluable. Designimprovements (Figure 9) a)Incorporation ofafailsafe release mechanism atthePiston/Leadscrew interface b)Ground tabsatthelinkages c)Lateralcompliance specifically designed intoeachlinkage assembly d)Damping attheshearpins NASA/C P--2002-211506 277
SafetyReleaseMechanism /Ground Tabs(3X) Figure9.Design Improvements Conclusion TheMDSprototype hasdemonstrated asimple, costeffective andreliable designthatisscaleable. The MDSwascreated intheabsence ofhardrequirements. Although thiswasoftenadifficult andfrustrating process, itallowed theblending oftechnology andvisiontocreateaverysimple, yeteffective, system. It wasnecessary toevaluate alltypesofpotential design solutions fromaveryhighlevelwithaderived mission objective inmind.Asshown through tradesandsystem testing, theapplication offewer mechanisms andtheuseofcommon proven technology (i.e.,motors, leadscrews, andlinkages) can resultinadesignwithaveryhighleveloffunctionality. Because ofthesecharacteristics, theMDShasthe potential tosupport avarietyoffuturemission requirements. NASA/CP--2002-211506 278
satellite(s). Ratesensors wereemployed tomeasure ratesinthepitch,roll,andyawaxesandalinear position transducer wasusedtocapture thestraight-line separation motion oftheunit.Datafromthese instruments werereadintoLabVIEW formanipulation andprocessing. Thebenefits ofusingthe automated separation reliability testprocedure aresubstantial whencompared totraditional methods of testing separation reliability. Background Li.qhtband Separation System TheLightband separation system isarecently developed mechanism. Itsadvances overexisting technology include lowweight, lowshock, lowprofile, lowcostandversatility. Planetary Systems Corporation substantially developed theLightband through funding fromaPhase Iandongoing Phase IIof aSmall Business Innovative Research grant, awarded bytheAirForce Research Lab.TheLightband successfully released andspun-up theStarshine-3 satellite fromtheAthena (Lockheed Martin) launch vehicle inSeptember 2001andismanifested onanother tenmissions. AUSpatent hasbeenawarded andthree derivative USandinternational patents arepending. Figure 1illustrates theessential components oftheLightband separation system. Separation Electrical Connectors allowsignalandpowerbetween adjoining vehicles. Theyemploy zero-force pinsforlowtip-offrates.UpperandLowerRin.qsarethe mechanical interface toadjoining vehicles.De-tensioner initiatesseparation by cuttingtheretaining linewith redundant radiantheaters. They arenonpyro-technic anddonot generate anygasordebris Tensioner setsthe Lightband forflightby tensioning theretaining line.Abuilt-inloadcell redundantly verifies readiness. Retaininq Lineundertension joinstheLightband rings.Precision Hinged'Leaf' unlatches androtatesto release. Grooves forshear pinseliminate dependence onfrictionforjointstrength. Precision Separation Sprin.qs impartseparation velocity. Springscanbeaddedformore velocityortocompensate forCG offsets. Angledspringscan produce spin-upifdesired. Figure 1.The38.1-cm (15-in) Diameter Advanced Lightband Separation System Theprocedure forsetting andoperating theLightband isstraightforward. Tomatethetworings,a retaining lineisbrought totension withatorque wrench andlatches thehinged leaves onthelowerring intoagroove intheupperring,asshown inFigure 2.Tension ismeasured byaloadcellandcanbe NASA/CP--2002-211506 280
adjusted atanytime.Toinitiateseparation, thede-tensioner isactivated andcutstheretaining lineby radiantly heating it,asshowninFigure3.Thecutlineretracts beforeitcanburnormelt,leaving nodebris andproducing nosafetyhazard. Redundant springplungers ateachleafunlatch androtatethehinged leaves, freeingthecompressed separation springs. Theseparation springs pushthehalvesapart,andthe separation connectors disengage asshowninFigure4. Figure2.Setting theLightband Figure3.Radiantly heating the Retaining LinetoBreakit ! Figure4.Lightband During Separation TheLightband's lowweight(onethirdofequally performing V-bands), lowprofile(oneeighththevolume ofaV-band), lowshock(anorderofmagnitude lessthanaV-band), andversatility havemanybenefits. Theyallowtallerspacevehicles, longersolararrays, largerexternal components inandaround the separation plane,andcustom interfaces withspacevehicles. TheLightband isthoroughly testedfor strength, stiffness, separation reliability, thermal vacuum, shock, andvibration, andallseparation subsystems arecompletely included. Separation Reliability Fixture Planetary Systems Corporation designed theseparation reliability testfixturespecifically fortheLightband separation system. Itconsists ofastationary frame(emulating thelaunchvehicle interface), andafivedegree offreedom displacing side(emulating theseparating satellite), asshown inFigure 5.The displacing sideiscomposed ofthreemainparts:amoveable armwithaframeinterface identical tothat onthestationary side,anairtank,andaglasstable.TheupperringoftheLightband isattached tothe displacing sideandthelowerringisattached tothestationary side.Airbearings provide frictionless motioninfiveaxes,fourplanarair-bearings allowing translational motionalongtheglasssurface intheX andYdirections, andaspherical air-bearing allowing rotational motionofthearminthepitch,roll,and yawaxes.Thereiscurrently nofreedom ofmotion inthevertical axis,preventing thefixturefromhaving freedom ofmotioninallaxes. NASA/CP--2002-211506 281
Spherical Airbearing AirTank PlanarAir bearings GlassDirectionof AngleofDisplacement Separation (Exaggerated toshow "_ / Degrees ofFreedom) Separating Arm_':. (Lightband UpperRing) jl(, __ ,,. Stationarym Side YAW iI"_o':(_, _ (LightbandLowerRing) ROLL,\&!I_ _"; Figure5.Separation Reliability Fixture Separation Reliability Fixture Components AirBearinq Assemblies Airbearings arefluidfilmbearings. Athinfilmofpressurized airformsalayerbetween theloadandthe contact surface, resulting infrictionless motionandnosolid-to-solid contact. Airbearings havenobearing wearandofferamuchhigherstiffness thanballbearings. Theyarealsoclean;usingonlypressurized air ratherthanoilasthelubricating fluid.Thesecharacteristics giveairbearings alargeadvantage overball bearings ineliminating gravitational torques. Atotaloffiveairbearings wereusedattwointerfaces onthe separation reliability fixturetoprovide frictionless motion. Fourplanarairbearings weremounted atthe baseoftheairtank,asshowninFigure6,toallowtranslational motionalongtheglasssurface intheX andYdirections. Aspherical airbearing, composed ofanupperhemisphere andalowerspherical air bearing socket, asshowninFigure7,waspositioned atthetank-arm interface toallowrotational motion ofthearminthepitch,roll,andyawaxes.Theairbearings arehydrostatic, andaredrivenbypressurized airat400-550 kPafromtheairtank,whichisperiodically refilledwitha3/4horsepower compressor. Planar AirBearings NASA/CP--2002-211506 282
Upper Hemisphere LowerSpherical AirBearing ....-_AirTankfV._ Figure7.SphericalAirBearingAllowsPitch,Roll,andYawMotion Angular RateSensors Angular ratesensors wereattached totheseparation reliability fixture, asshowninFigure8,andwere oriented tomeasure pitch,roll,andyawratesuponseparation. Special attention waspaidtothewires connecting theratesensors totheLabVIEW dataacquisition (DAQ)program. Thefrictionless motion produced bytheairbearings created anenvironment highlysensitive totorques, bothfromtheseparation eventandfromunwanted external factors. Theseunwanted torques included thosegenerated bydangling wiresfromtheratesensors. Thinandlightweight wires(32AWG)wereusedtominimize anytorques of thistype,though thedecreased wiresizemayhavecontributed toanincrease inelectrical signalnoise. Thiswirechoicedidincrease thefragility ofthesystem, astherewereaccidental wirebreaksthatwould nothaveoccurred withmorerobustwire.Increasing thesizeoftheconnection wires,andrepositioning the wirestoconnect vertically totheseparation reliability fixtureratherthanfromtheside,mayleadtobetter system performance. Pitch RateSensor ,_::__,-:T YawSensor notshown ,_,:__,_,J'_,',:_ Roll ,.}_,_ ,._ RateS_ __  /WirestoRate ___ /Sensors Figure8.Angular RateSensors Measure RatesAboutthePitch,Roll,andYawAxes Velocity Measurement UsinqLinearPosition Transducer Ahigh-performance linearposition transducer wasusedtomeasure translational velocity. Itwasmounted onthestationary sideofthefixtureandoriented alongthetranslational pathofseparation, asshownin Figure9.Thelinearposition transducer wasconnected totheseparating sideofthefixturebyapieceof NASA/CP--2002-211506 283
string,asshowninFigure10.Thecontribution offrictionwithinthemotionofthetransducer tothe separationvelocitymeasurement wasinsignificant. Thetransducer hadarangeof15.24cm(6in)of travel,andwasconnectedtotheseparating sideofthefixturesuchthatthisrangeofmotionwasnot exceeded.ThevoltagesignalfromthetransducerwasconnecteddirectlytoLabVIEW. hightband _ _'i_.--[t'_v-_m_ _'_".t..y .,. LowerRing __ " ':"!I__ ",' ._::,i_q (,,_,," " Lightband_::_ ,'-_,. . : UpperRingExten .'_ : Linear __',._._ _,",":;_:, Trans_n,cerPOSition,.,,., .... ': l"F_.,:._,:i:__:_";............... ._ Figure10.LinearPosition Transducer (post-separation event) Emulating MassProperties Toaccurately testandcharacterize theseparation event,themassproperties ofthedisplacing sideofthe fixturewerematched closely tothoseofthesatellite tobeflown.ABi-filarpendulum wasusedto experimentally determine themoment ofinertiaofthefixture, asshowninFigure11.Changes tothe fixture's moment ofinertiawereexecuted byaddinganoutrigger totheseparating armandvarying mass, bothontheoutrigger andontheairtank,asshowninFigure12. NASA/CP--2002-211506 284
'ii Pendulum, Figure11.BifilarPendulum toMeasure Moment ofInertiaThin Filament _i_Outrigger for !i_Moment ofInertia Additional Mass Figure12.MassProperties ofFixture Matching themoment ofinertiaintherollaxiswascriticalforStarshine-3, astheLightband notonlyacted asaseparation system butalsoimparted adesired orbitspintothesatellite. Thisspinwasachieved through angledseparation springs. Determining thespringconfiguration necessary toachieve thedesired spinof5degrees persecond wasexperimentally possible because oftheclosely matching moment of inertia. Earlyspin-up predictions forStarshine-3, derived fromangular ratedataacquired whenthe displacing sidehadamoment ofinertiadifferent fromthatofthesatellite, werefoundtobeinaccurate. Simply acquiring angular ratedataforasystem withaknownmoment ofinertia, andthenusingthe principle ofconservation ofangular momentum tocalculate theequivalent angular rateforasystem witha different moment ofinertia, should bestraightforward. Forreasons thatarebeyond thescopeofthis paper,thisreal-world system didnotfollowtheprinciple ofconservation ofangular momentum, anditwas necessary tomatchthemoment ofinertiaofthedisplacing sideofthefixturetoStarshine-3 toaccurately predicton-orbit spin. Balancin.q theTestFixture Because thetestfixtureisanearlyfrictionless system, itisessential thattheseparating armbeexactly balanced. Anyuneven massdistribution around thepitch,roll,oryawaxeswouldcausedriftand acceleration duetogravity, andwouldcompromise theexperimental testdata.Theseparating armwas balanced through aniterative process ofmassdistribution. Theinitialbalancing stagetookplaceoncethe upperringoftheLightband wasboltedontotheseparating armandtheairtankwasfilledwith compressed air,allowing thearmtomovefreely.Thearmwasplacedina"neutral" position (roughly level andnotincontact withanything otherthanthespherical airbearing) andheldasmotionless aspossible. Uponrelease, themovement ofthearmwasobserved andnecessary massdistribution adjustments were NASA/CP--2002-211506 285
made.Balanceadjustments generallybeganwithlargerunitsofmass,suchasthesubtraction and additionofsteelplates,andevolvedintosmalleradjustments usingsmallerunitsofmass,suchas washersandbolts.Finalbalancerefinements wereachievedwithVerniercenterofmassadjustment screws,asshowninFigure13,andcontinueduntilthearmremainedasmotionless aspossibleupon release.Thearmwasalsoplacedin"tilted"startingpositions(roughlylevelbutnowrolled-45degreesto therightortheleft)andalsoreleasedandobserved.Additionaladjustments weremadeasneeded. VernierCenterof MassAdjustment Screws Figure13.VernierCenterofMassAdjustment Screws Instrument Calibration Ratesensor calibration wasperformed beforetesting. Thereweretwomethods ofcalibration used,a pendulum-based LabVIEW program andastopwatch-timed manual procedure. ForthependulumLabVlEW program, apotentiometer wasattached totherotation axelofasimpleone-degree offreedom pendulum, andtheratesensor tobecalibrated wasattached atalowerpointalongthependulum as showninFigure14.Datafromthepotentiometer, whichgavetheangleofthependulum withrespect to time,werecompared todatafromtheratesensor, whichgavetheangular rateofthependulum with respect totime.Theratesensor datawereintegrated anditscalibration factorwasthenvariedtomatch theoutputofthepotentiometer. ThisisshowninFigure15. Axisof ..........", _: Rotation .- Pendulum Arm RateSensor Tobe CalibratedPotentiometer Figure14.RateSensor Calibration Pendulum NASA/CP--2002-211506 286
E15 10 -5 -10 -15RateSensor Calibration Test,Deg/sec/Volt=25.7 i 5 Time[sec]l IPotentiometer i Integrated RateSensor Figure15.RateSensor Calibration Data Thestopwatch-timed procedure involves manually turning theairbearing armataknownrateofrotation andcomparing thatratetotheonerecorded bytheratesensor. Bothmethods wereusedtoensure correct ratesensor calibration. Thecalibration ofthelinearpotentiometer wasperiodically checked by extending theshaftataknownvelocity andcomparing thattothecalculated speed. LabVIEW Proqram andCode LAbVIEW programs werewrittentoautomate theseparation reliability procedure oncetheLightband was physically mated. These functions included verifying thereadiness ofallelectrical connections and instruments priortotest,initiating theseparation event,characterizing theseparation eventthrough data acquisition fromtheattached sensors, timingtheeventfrominitialization ofthedetensioner toactual separation, andturning thedetensioner offonceseparation tookplace.Programming inLabVIEW was relatively simple, though gaining familiarity withthesoftware anddeveloping anddebugging thedata acquisition programs tookasignificant amount oftime.Signals fromtheratesensors weredirectly connected totheLabVIEW DAQcard,aswastheLightband separation connector. Thebenefits ofusing LabVIEW toautomate theseparation reliability testprocedure include highrepeatability, automatic data logging andanalysis, low-cost dataacquisition, andflexibility. TestdatafromLabVIEW wasoutputtothe serverandcouldbeimmediately scrutinized toverifypredictions anddetermine whichadditional changes werenecessary tomeetseparation requirements. Asystem blockdiagram ofthedataflow isincluded as Figure16. Electronics Anelectronic circuitwasbuilttoincorporate thesensors andLightband components intoanautomated dataacquisition system operated inLabVIEW. Thecircuitallowed signals fromthevarious sensors tobe inputintoLabVIEW andalsocontrolled theseparation eventitselfbyapplying voltage tothedetensioner in aprescribed sequence. Accurate timingoftheseparation eventwasdetermined bycomparing thetime thedetensioner wasinitiated tothetimeoftheseparation connectors lostcontinuity, whichwasreadby monitoring theseparation connector signal.Allofthesensors operated ataregulated 5volts,and12volt batteries wereusedastheoriginal powersource inanefforttoreducenoiseoriginating fromthesensors' excitation voltage. Thismethod worked well,though itwasnecessary tocontinually checkandrecharge thebatteries asaweakened excitation voltage couldproduce falseoutputsignallevels.Anopto-isolator chipwasusedtoisolatethepowersupplyusedtodrivethedetensioner fromtheLabVIEW inputsignals. Thisremoved anychance ofthepowersupplydamaging orinterfering withtherestofthecircuitry and hardware. NASA/CP--2002-211506 287