ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Sun Turnbuckle _-_<_'_ it'_ii Location (2)XtI__ _-__'_--_ _'___  t/;','/ CordStando_ ,/t1ti4'\,il! r/\!/H/' Location (12)_i/ 1"[11./ _!/i]/// _ _,v-. ll'1 The  o, bolar_anel,/__]\,t'L,' CellSide "--_-_--[ Knifewith KevlarCord mount location (2) Figure2.SARRS Configuration (Instrument notshown) Twocordstandoffs, shownindetailinFigure3,arepositioned ontheouteredges;ofeachsolarpanel. Thestandoffs positionthecord33mm(1.3in)abovethesolarcellsinordertoprovideenoughclearance infrontofthesolarcellssuchthatthecordwillnotcontactanddamage thecellsduringrelease. I ,,i:_-_..........I_Iz Solar /w1iII_,_>-:l...--::_...... CellArea .,_-.-._LI-_-_.._/--, Figure3.CordStandoff withKevlarCord TherearetwothermalknivesintheSARRS. Eachknifeisheldinamount,showninFigure4,whichis attached tooneoftwosolarpanelsonopposite sidesofthespacecraft. Thecordstandoffs andmounts arepositioned suchthatthecordremains incontactwiththethermal knifeheaterelement, whichis pressed towards theKevlar cordbyaspringwithinthethermal knifecomponent. Mount _ /Thermal Knife Heater Cord Element Figure4.Thermal KnifeinMount Todeploythesolarpanels, powerisapplied toeitherofthetwothermal knives,whichgenerate temperatures inexcessof1000°Catthetipoftheirrespective heatingelements. Thethermalknifethen NASA/CP--2002-211506 245
beginstosevertheKevlarcordbymelting through thefibers,degrading thetensilestrength oftheKevlar cord.Thedegradation continues untilcord'sstrainenergysuddenly breakstheremaining fibers,allowing thecordtoflyfreeofthespacecraft, releasing thepanels. KevlarCordConfiquration Thecordassembly isconstructed oftwoKevlarcordsections, each3.8m(150in)inlength,thatare joinedbytwoturnbuckles madefromtitanium, asshown inFigure5.Theturnbuckles areusedto increase thecordtension duringinstallation, astheKevlarcordrequires alargestrain,about300mm(12 in)toachieve thepropertension. TheKevlarcordisconstructed ofwovenKevlarfibersthatareatvarious angleswithrespect tothetension load.Whentension isapplied, thefiberstrytoalignthemselves along theloaddirection andextendthecordlength. However, itwasfoundthatpre-stretching theKevlarcord wouldincrease thecordstiffness, thusrequiring ashorter turnbuckle toachieve thesameload.After assembly, thecordwaspre-stretched bycycling thecordwitha157N(700Ib)load10timesfor3min eachtime.Thisprocess isdiscussed inmoredetailintheKevlarCordBehavior section below. Theturnbuckles arelocated between thesolarpanelsintwolocations 180degrees apartand90degrees awayfromthethermal knives, asshowninFigure2.Theadvantages ofthisconfiguration areamore distributed cordloadduringtensioning andthemitigation ofpotential solarcelldamage duringcord release. Threaded Clevis Attachment Kevlar Figure 5.KevlarCordwithTurnbuckles Inaddition togenerating largestrain,theKevlarcordweave pattern generates acompressive force towards thecordcenterwhentension loadisapplied. Thisbehavior enables theKevlarcordtobe attached totheturnbuckle withasimplebuteffective loopthatreliesentirely oninternal frictional forces fromthebraided pattern, asshown inFigure6.Thisdesign allowsacordassembly todevelop its maximum breaking strength characteristics byavoiding strength reducing knots. Compressive forces generated fromtension  loadingholdscordendin ------j Threaded Clevis  TensionLoad Figure6.KevlartoTurnbuckle Attachment KevlarCordRelease Mechanism" Thermal Knife Thethermal knifewasoriginally developed byFokker Space andhassuccessfully beenusedon numerous flightprograms. Thethermal knifecomponent wasselected aspartoftheSARRS duringthe initialdesignphase. Itwasalsodecided thattherewouldbenomodifications madetothethermal knife NASA/CP--2002-211506 246
becauseofitssuccessfulflightheritage.However,thedifferences intheknife'sutilizationintheSARRS wouldrequireanextensivedevelopment andtestprogram. Thermal KnifeDescription Thethermal knife(T/K)consists ofaceramic substrate heaterelement, 8xl0x0.7mm(0.3x0.4x0.03 in), withdualelectrical resistance tracepatterns. Thetracepatterns heatthesubstrate totemperatures in excess of1000°C.Twopinssupport theheaterelement andprovide theelectrical powertotheparallel tracepatterns. Thepinsandheaterelement areheldinacylindrical housing andaspringinsidethe housing preloads theheaterelement topushitagainst theKevlarcordduringthecuttingprocess. Figure7.T/KHeater Element withTraceFigure8.Thermal Knife T/KUse TheMAPSARRS usesaredundant thermal knifeconfiguration thatisdifferent thanprevious thermal kniferelease system designs. Thisdesign allowseitherknifetooperate andrelease thesystem. In addition, theoperation ofoneknifewillnotdamage theredundant knifeandafailure(electrical or mechanical) willnotinterfere withoperation oftheotherknife. TraceDamaqe Thethermal knifetracematerial becomes softwhenthesubstrate isheated andismoresusceptible to damage duringthisperiod. Itisimportant tomaintain minimum contact between theKevlarcordandtrace duringthecutting process. FortheMAPSARRS, minimum contact isachieved byusingaminimum diameter Kevlarcord,largestrainvalue,andacontinuous 90-degree angular contact configuration between thecordandheaterelement. TheSARRS Kevlarcordislessthan3mm(0.12in)indiameter. Thisrelatively smalldiameter combined withlargestrainallowstheKevlarfiberstopullawayfromthetraceduringthecuttingprocess, asshown inFigure9.Onthecontrary, asmaller strainvalueandlargercorddiameter causes thesevered fiber endstoadhere tothetraceduringactivation andinsomeinstances pullthetraceoffthesubstrate when theKevlarcordiscompletely severed andseparates, asshowninFigure10.Inthisinstance, theKevlar cuttingprocess wouldnotbeaffected duringtheinitialtracedamage, however, allsubsequent cutswould beaffected byanalready damaged trace. 44-_,'<cxxxxxxxxx_y_ TraceElernent ,-""Vii (parallel circuits) IL____Heater ElementSubstrate Figure9.T/KElement andSmallDiameter KevlarwithLargeStrainKevlar(MAPdesign)Figure10.T/KElement andLargeDiameter KevlarwithLowStrain NASA/CP--2002-211506 247
IntheMAPSARRSdesign,theKevlarcordmaintainsanear90-degreeanglewiththeheaterelement surface,asshowninFigure11.Asthetraceelementislocatedclosetosubstrateedge,alessthan90degreeanglebringsthecordclosertotheheaterelementtrace,asinFigure12.Withthisconfiguration, thereisanincreasedriskofdamagingthetraceastheKevlarcordtravelsaroundtheheaterelement edge.Thedamagetothetraceoccursoncethefibershavebeensevered,thusthedamagewouldnot becomeapparentuntilthesubsequent activation. / Figure11.MAPSARRS T/KandKevlarCord Configuration_T:_ _P.vlar,::ordnear I_1 "tI-aCP_, element in,:reasesiisic,_,::,f t.l"aI-:_e.(taI[1age Figure12.T/KwithKevlarCordLessthan 90-degree Angle Wheninspecting theknifeafteracut,acontinuity checkmaynotrevealthepresences oftracedamage in allcases.Aresistance measurement mustbemadetoinsuretheelectrical integrity. Inaddition, forthe MAPSARRS, avisualinspection (20Xmagnification) wasperformed priortoandafterfinalground activation toinsuretraceintegrity. Theinspection waspossible because theSARRS design allowsthe thermal knifeheaterelement tobeexposed afteritseversthecord.Along-range microscope wasusedto inspect andrecordthetracecondition. TheMAPSARRS neverexperienced thepotential thermal knifeproblems citedaboveoranyother problems, duetoitsthermal knifeconfiguration. However, therehavebeensomeissueswiththethermal knifeonotherprojects. Afterthoseprojects investigated theirproblems, solutions weresuggested, butthe SARRS wasalready incompliance withthosesuggestions. Thus,theMAPSARRS configuration has beensupported bymuchmoreinformation thancanbepresented underthescopeofMAP,andthose datawillmostlikelybepresented inthefuture. KevlarCordBehavior TheSARRS cordtension requirement wasboundbyminimum andmaximum valuesof45N(200Ib)and 110N(490Ib),respectively. Theminimum tension wasthetension required tosecure thesolarpanels against theirstopssuchthatgapping didnotoccurduringlaunch. Themaximum valuewasbasedonthe spacecraft structure's abilitytowithstand thecompression induced bythecordtension. Inaddition, the tension mustbemaintained abovetheminimum for45daysonthelaunch padandduringthelaunch environment. Aseriesoftestswereperformed todetermine theKevlarcordtension characteristics under theseconditions. Time,pre-conditioning, humidity, andtemperature allaffecttheSARRS Kevlar tension toadand relaxation rate.Aseriesoftestswereperformed toinvestigate theindividual andcombined effectsthat eachoftheseconditions wouldhaveontheKevlarcordtension. Thecordassembly hasatotalunloaded lengthof7.62m(300in).Itwasnotfeasible toplacethisentire lengthwithintheavailable testchamber. Therefore, atestwasperformed toinvestigate thefeasibility of testing shorter cordlengths andapplying theresults tolongerlengths. Theseresults proved tobe positive, soitwasdecided toproceed withtestingusingcordsamples thatwereshorter thantheflight cords. Relaxation FromFinalStowaqe ToOn-orbit Deployment Earlytesting showed thattheKevlarcord,asdelivered, wouldlosetension veryrapidlywithrespect to time.Inanefforttoreducethetension lossovertime,apre-conditioning, orpre-stretching, process was NASA/CP--2002-211506 248
developedandimprovedduringthedevelopment oftheSARRS.Thefinalprocessinvolvedpre-stretching thecordbytensioningitwith157N(700Ib)10timesfor3mineachtime.Thenitwasinstalledonthe spacecraftandtensionedtotheinitialtension.Afteratleast24hours,thecordwasre-tensioned toits initialtension.Variationsofthisprocessareevidentthroughoutthecharacterization processasthisfinal processwasderived. SeveraltestswereperformedthatsubjectedtensionedKevlarcordsamplestoasimulatedenvironment fromcordinstallation toon-orbitdeployment. Theinitialpurposeofthesetestswastodeterminethe relaxationrateandfinalcordtensionattheendofa45-dayperiod.Later,thetestwasextendedto includethelaunchenvironment. Thegoalwastodemonstrate thatapre-stretched Kevlarcordcould maintainaminimumtensionof45N(200Ib)throughouttherequiredtimeinterval. AKevlartestspecimenof41cm(16in)wasusedinthefirsttest.AtypicaltestfixturewithKevlarcord specimenandloadcellisshowninFigure13.Thespecimenwaspre-stretched bycyclingthetensionto 112N(500Ib)tentimesatthreeminutesdurationandimmediately placedinthetestfixtureat62N(275 Ib).Twodaysaftertheinitialloading,arelaxationplot,Figure14,projectedthatthecordwouldnot maintaintheminimumtensionfortherequired45-dayperiod.Thespecimenwasreloadedtoitsinitial valueandanew45-dayperiodwasstarted. LoadCell  / /KevlarTestSpecimen Figure13.LoadRelaxation TestFixture Duringthefirst10daysofthenewcycleitbecame apparent thattheambient humidity fluctuations were affecting theloadrelaxation rate.Todetermine themagnitude ofthehumidity effects, thespecimen was placed inahumidity-controlled ("Glove") boxsothetension loadcouldbemonitored asafunction of relative humidity. Eachtimethehumidity setting waschanged, thecordloadreadings wouldchange according toapproximately 0.5N(2.5Ib)per%change inrelative humidity (RH).Atday24theRHwas setto40%fortheremaining duration ofthetest.Therateofrelaxation duringthisperiodwasconstant. LoadChanqe inVacuum Anadditional testtosimulate thelaunch environment wasconducted withtwo64cm(25in)Kevlar specimens. Thespecimens wereexposed tofullvacuum within10minutes (37%RHto0%RH)after beingpre-stretched (10times/3 minduration with112N)andthenloadedto70N(310Ib).Thetotalload lossforbothspecimens was17N(75Ib)after24hours,orapproximately 0.5N(2Ib)perpercent humidity. Figure15illustrates therateoftension losswhilethecordwasundervacuum. NASA/CP--2002-211506 249
Load (Ibs)300 ,'''i.... i.... i.... i''' 16"Specimen 2_o 60%RH t_ Placed inGIo_e Box 260 Ft_,._/40 %RH 240 _.30 %RH 40%RH -- Initial Loading 1k 200 0 10 20 30 40 50 -rime(days) Figure 14.LoadOverTimewithVarying Relative Humidity Load (lbs)320 300 280 260 240,i 2'iI,, i,,i ,i.... i.... i.... _Vacuum Loa_dLossData A A i#12 /" #13 • AA 220 .... ''''I,,,,I,,,,I,,,,t,,,, 0 5 10 15 20 25 30 Time(hrs) Figure 15.Kevlar Tension Lossunder Vacuum Relaxation RateVersus TimewithConstant Relative Humidity Atestwasdesigned todetermine theSARRS cordrelaxation rateandwhether theinitialtension load wouldaffecttherate.FourKevlar cordspecimens 64cm(25in)werepreloaded 10timeseachto157N (700Ib)for3minutes duration. Thecordsweretensioned to74,80,85,and91Ninahumidity environment of-40%RH.Itwasnotedthatpriortoplacing thespecimens inthetestchamber the tension wasdecreasing rapidly. Thetensions werereloaded totheirinitialvalues threetimeswithina50minute period. Eachtimethespecimens werereloaded therelaxation ratedecreased. Afterthethird reloading, thespecimens wereplaced inanenclosed environment thatmaintained 22-24°Cat50%RH. Thetension values werecontinuously monitored for45daysandtheresults areshown inFigure 16. Theloadswereplotted verses timeonalogarithmic scale.Theloadincrease atday9resulted froman errorinthetestchamber humidity setting. Fromtheplot,therateofrelaxation wasindependent ofthe initialtension anddecreased anaverage of5%perorderofmagnitude. Based ontheslope, thecordlost 5%oftheinitialtension withinthefirstday,another 5%byday10,andanother projected 5%byday100 afterthefinalreloading. Thus,thecordwouldloselessthan15%ofifitsinitialtension after45days. NASA/CP--2002-211506 250
Load (Ibs)400 38O 36O 340 32O 300 280 260,_--Humidity setto50%RH ........ i  :add t ike,,,Li=ill liiliIAll ii,iiii O.1 I 10 O0 Time(days) Figure16.45-Day CordRelaxation Rate Temperature Effects Atestwasperformed todetermine thetemperature effects ontheSARRS cord.Atypicalloadversus temperature plotwasgenerated fromtemperature andloadprofiledata,asinFigure17.Below40°Cthe Kevlartension changed atarateof0.2N(0.9Ib)perdegree Celsius andtherateofchange above40°C wasless,soitwasassumed tobezero. 420.,,,_,1-,I'',[,,rI''•[''_.L....J.....-._ • 400! ..........................! 380 Load i (Ibs) 360 34017............ ..... 320 i i -60 -40 -20 0 20 40 60 80 Tempcrature (C) Figure 17.Loadvs.Temperature CordTension Prediction Therewasnoaccess tomonitor thecordtension afterfairinginstallation andduringthepotential 45days onthelaunchpad.However, itwaspossible toestimate theSARRS cordtension atanypointfromthe lastmeasurement todeployment. Thecalculations werebasedontheabovetestresultsofrelaxation ratesduetotime,relative humidity changes, andtemperature (Table1). NASA/CP--2002-211506 251
Table1.Calculating theResultant CordTension GiventheEnvironment Asanexample, given: Installation Tension Humidity duringinstallation TimeonlaunchPad Humidity during10dayperiod PadTemperature OrbitTemperature Deployment in1.5hours76.4N(340Ib) 46%RH 10days 40%RH 18°C 35°CTheminimum tension duringlaunchwouldbe: Installation Tension Change in%RH(6x0.5N) TimeonPad(0.1x76.4N) Vacuum (3.3N/hr) DeltaTemperature (17°C)76.4N(340Ib) -3.3N(15Ib) -7.6N(34Ib) -5.2N(23Ib) +3.3N(15Ib) Minimum Launch Tension 63.6N(283Ib) KevlarCordTension Measurement Asdescribed intheBackground Section, theMAPSARRS reliesonaKevlarcordtorestrain thesixsolar panels intheirstowed configuration duringlaunch. Thecordmustmaintain aminimum tension to eliminate vibration impactbetween thesolarpanelsandthespacecraft busduringlaunchandtoflyaway fromtheprobewhenreleased. Inaddition, theminimum tension mustbemaintained foratleast45days incaseoflaunch delays. DuringSARRS development, itwasfoundthattheKevlarcordhasacreep characteristic thatcauses ittorelaxandloosetension overtimeasdiscussed inthesection above. In ordertohelpcharacterize thecreepcharacteristic andtoensure thattheproperinitialtension isapplied tothecordbeforelaunch, accurate andreliable tension measurements hadtobemade. Issues Itwassoondiscovered thattheoriginal method employed tomeasure thecordtension, theuseofa three-point tensiometer, theonlycommonly usedmethod ofmeasuring cabletension, provedtonotwork forKevlarcord. Three-point tensiometers areusedinthestandard method tomeasure thetension instainless steel cables. Thesehand-held devices measure acable's tension bybending itaround twopostsandaplunger asshowninFigure18.Thedevicemeasures theforceontheplunger fromthebentcableandachart calibrated specifically forthetypeandweaveofthecabletranslates thisforceintothetension inthe cable.Thismethod workswellforstainless steelcables. Plunger '_ bl Cable "_ _/_A _ Cae Post Post Figure18.ThreePointTensiometer Schematic However, itwasfoundthataTensitron three-point tensiometer didnotworkwellwiththeKevlarcord.Its measurements variedby17%alongonecontinuous, section ofcord,supported onlyattheends,where thetension isactually thesamealongtheentiresection. Also,repeated tension measurements madeby thetensiometer inthesamelocation onthecordvariedbyupto10%. Observation ofthecordafteratension measurement bythetensiometer revealed thatthetensiometer waspermanently deforming thecordandleaving acrimp,resulting inmeasurement errors.Also,the tensiometer attempted toincrease thelengthofthecordduringmeasurement bystretching it,butthe frictionatthecordstandoffs didnotallowforthestretching forcetobeabsorbed bytheentirelengthof thecord,and,thus,greatly increased thetension inthelocalsection beingmeasured. Thecrimpandthe frictionphenomena ledtothebeliefthattheproblem waswiththemethod ofthethree-point tensiometer, ratherthantheparticular deviceitself. NASA/CP--2002-211506 252
Basedontheseissues,itisnotpossibleforthethree-point tensiometer tomeasuretheKevlarcord tensionsufficientlytomeetMAP'srequirements andmustbereplaced.Anotherexistingmeasurement methodcouldnotbefoundforKevlar,soanewmethodwasdevelopedtomeetthesystemrequirements. Solution Thedevelopment ofanewtension measurement system beganwiththefollowing designrequirements: •Measure thetension intheKevlarcordtowithinplusorminus4percent withinthedesired 22 to101N(100to450Ib)range •Repeatedly measure thetension inthecordwithinthesamesection withinthegiven tolerance range •Becapable ofsinglehandusethatcansafelybeusedtomeasure thecordwithinclose proximity totheflightsolarpanelswithminimal risktotheflighthardware Afterconsidering afewotheroptions, arathersimple solution wasfound,theMusical PitchMethod (MPM). TheMPMusesaninnovative process toaccurately measure tension incordsmadefromKevlar bycombing musictheoryandphysics relations. TheMPMemploys anoff-the-shelf chromatic tunerwithaclip-onpick-up, atypeofmicrophone, shownin Figure 19,todetermine thetension inKevlar cord.Musicians usethesetuners totunemusical instruments. Thechromatic tunermeasures themusical note,orpitch,thatemanates fromafreesection ofcordwithfixedendconditions whenplucked likeaguitarstring.Thetuner'smicrophone canmeasure thepitch,buttheclip-on pick-up eliminates theeffectofbackground noise.Musictheoryassigns a frequency toeachmusical pitch,so,bymeasuring thepitch,thetunermeasures thefrequency ofthe vibrating cord.Aphysics formula translates thefrequency tothetension basedthesection's nodelength andthecord'smassperunitlength. Figure 19.Thechromatic tunerwiththeclip-on pick-up Frequency Measurement Thechromatic tunermeasures musical pitches byproviding information abouttheoctave, note,andcent deviation fromaperfect musical note.Themusical noteinformation mustthenbetranslated into frequency measurements viamusictheorydefinitions. Eachmusical notehasanassigned frequency. Bydefinition, theAabovemiddle Crepresents a frequency of440hertz(Hz).Twelve notesformanoctave, C,C#,D,D#,E,F,F#,G,G#,A,A#,B,with the#representing asharp,soC#isCsharp.Similarly named notesindifferent octaves represent frequencies thatdifferbyamultiple oftwo.Forexample, theAintheoctavebelowmiddleCrepresents a frequency of220Hz.Thissequence repeats itselfinthenextoctave. Thestepsbetween eachofthe twelvenotesareknownashalfsteps.NoticethatB#orE#donotexist.Thatisbecause thereisanatural halfstepbetween E,FandB,C.Thefrequency ofeachnotebetween theAinoneoctaveandtheAin thenextoctavearedetermined bytheproperfraction ofamultiple oftwo.Forexample, thefrequency of theA#abovetheAwithafrequency of440Hzisdetermined by440*(2(1/12))=466.1.Table2showsthe frequency thateachnoterepresents forthethreeoctaves withinMAP'sKevlarcordtension range. NASA/CP--2002-211506 253
Table2.Frequencies thateachmusical noterepresents inoctaves -1,0,and1 LowOctave (-1) Note Frequency (Hz) C 130.8 C# 138.6 D 146.8 D# 155.5 E 164.8 F 174.6 F# 185.0 G 196.0 G# 207.6 A 220.0 A# 233.1 B 246.9Middle Octave (0) Note Frequency (Hz) C 261.6 C# 277.2 D 293.6 D# 311.1 E 329.6 F 349.2 F# 370.0 G 392.0 G# 415.3 A 440.0 A# 466.1 B 493.8HighOctave (+1) Note Frequency (Hz) C 523.2 C# 554.3 D 587.3 D# 622.2 E 659.2 F 698.4 F# 739.9 G 783.9 G# 830.5 A 879.9 A# 932.2 B 987.7 Ameasured pitchcandeviate fromaperfectmusical tone.Thechromatic tunergivesreadings intermsof centdeviations thatrangefrom-50to+50.Thecentscalecorresponds topercent, butdiffers numerically, asthecentreading equalsthepercent distance between twonotes.Thecentsizedoesnot relatetothepercent deviation fromthefrequency ofthenotemeasured. Thecentsizediffersdepending onwhichnotesthemeasurement spans.IfthetunerreadsC+50cent,thepitchtieshalfway between aC andaC#and,inturn,thefrequency lieshalfway between thefrequencies foraCandaC#.Ifthetuner readsC+30cent,thenthemeasured toneis30%ofthedistance between CandC#fromC,andthe frequency equalsthatofCplus30%timesthedifference inthefrequencies ofC#andC.Thepitchand frequencies forC+50 centandC#-50centareequal. Table 3shows thefrequencies forthecentvalues between middleCandC#. Table3.Frequencies forthecentvalues between middle CandC# Note(cent) C C-(+10) c-(+20) c-(+30) C-(+40) C-(+50) C#-(-50) C#-(-40) c#-(-30) c#-(-20) c#-(-io) C#Frequency (Hz) 261.6 263.2 264.7 266.3 267.8 269.4 269.4 270.9 272.5 274.0 275.6 277.2 Tension Conversion Nowthatthefrequency ofthesection ofcordisknown, Equation 1,whichisderived fromthewave equation, canbeusedtodetermine thecordtension. InEquation 1,theTension Tisdependent onthe frequency y,thenodelengthL,andthemassperunitlength_ofthesection ofcord. (2yL)2/ -T (1) Equation 1represents thegeneral caseanddoesnottakestiffness orfrictionintoaccount. Itispossible tosolvethewaveequation forthetension inthestringwhiletakingintoaccount thesefactors, butthe solution iscumbersome andcorrection factors arestillneeded because ofmanyvariables inthe construction ofthecord(i.e.,weave, pre-stretch). Inordertocalibrate theMPMfortheparticular properties ofthecordusedforMAP,testswereperformed bytensioning asample section ofcordtoknownvaluesandmeasuring thetension withtheMPM.Charts couldthenbemadethatcalibrated thechromatic tunerreadings withthepropertension inthecord,as NASA/CP--2002-211506 254