ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
position andtheflowerrestsagainst theACTstatorstructure. Therefore, thecompression springs donot causeanyloadsonthebearings ormotorassembly inthereleased state. Onedesignrequirement change affected theMarman clampdesign. Thelimitloadarosefrom28g'sto56 g'sandthen,afterthere-design effortoftheMarman clamp,wentbackdownto28g's. Thestructure ofthelatchringissignificantly different fromthecommon typeofMarman-clamps. Usually several smallclampsarepressed withtheaidofatensioned steelbandbutherewehaveacircular aluminum clampthatitselfistensioned. Thisisbecause thelatchringradiuswaslimitedto92mm,which isverysmallrelative toexternal loads,anditisnecessary toutilizethecomplete circumference. Asimilar designhasbeenusedintheattachment ofsmallsatellites totheOSCPegasus rocket. Whenunlatched, thelatchringisrequired toextendbyitselfandbe2mmlargerindiameter thantheACT flanges. Thisrequires 31mmtangential expansion. Theexpanded ringispulledbytension springs torest against theshelves (Figure2).Theshelves guarantee thattheringwillnotinterfere withtheACTstator(the openMarman clamprotateswiththerotor). Duringdevelopment, several materials weretestedinvibration testsinwhicharepresentative latch configuration andaCAPSmassdummy withacorrectCoGwereshaken upto15gsinusoidal acceleration. Thefirstfundamental frequency withtheCAPSmassdummy wasdemonstrated tobeabove 100Hz.Thiscorresponded wellwiththeeigenfrequencies solvedfromtheFE-model byI-DEAS. During thesetwoprojects, theuseofI-DEAS waswidened fromthermal designtomechanical designand structural analysis (eigenfrequencies, staticstressanalysis) usingseveral UNIXworkstations. Moreofthe detaildesignworkshiftedfromdrafters toengineers. Thefirstlatchconfiguration consisted ofananodized AA6061 W-band latchpressed against Alodine 1200 treatedAA6061 flanges. Thecontacting surfaces oftheMarman clampweremadeconvexwith5-ramradii whiletheflangesurfaces wereplanar. Thisguarantees asmooth andcontinuous contact linearoundthe entirering.Avibration testshowed thattheanodized basematerial wasnotstrongenough andthe anodizing brokeoff.Also,theflangesurfaces weredamaged. Several material pairswithmodified geometrical properties weretested. Results areshowninTable2. Table2.Marman clampmaterials andgeometry. Actuator flangematerial Marman clamp Problems Comments innersurface Alodine treatedAA6061 Alodine treatedAA6061 60I_mHard-Anodized AA2219 60#mHard-Anodized AA2219 AA2219NorylGF30% plastic AISI316Steel AISI316Steel PEEKplastic, 1 mmthick PEEKplasticNorytistoobrittleand generated debris Steelsurface broke, anodized surface brokeoff fromthealuminum 56MPasurface pressure, somepermanent depressions. OK 56MPasurface pressure, somepermanent depressions: OKReduce surface pressure. Increase radii(R)of contact surfaces R=25mm R=25mm.Thechosen designY Lockinq mechanism Another unusual character oftheclampringisthelockingmechanism. Theclampisfullyre-latchable and opened byaHOPactuator fromStarsys. TheHOPactuator opensthelatchactuating mechanism (LAM) bypushing asmallhookforward andthusreleasing alockingpinonalever.Theleverisapartofanover257
centermechanism thatisusedtoreducea5000-NtensionforceintheMarmanclampdownto65Natthe lockingpin.Themovementofthehookisperpendicular toexternalforcesatthepinandthereforeitcannot openbyitself. Analysisoftheover-the-center mechanism revealedaproblemoffrictioninmechanism joints.Smallforces actingonthelockingpinrequiresthatthelatchringtensioningforcemustactveryclosetothepivotcenter. Thismakesthelatchopeningtorqueverysmall.Atthesametime,thetensioningforceonthepivotand levershaftremainsat5000Nthatcanhavelargefrictiontorque,ttisclearthatnoslidingbearingor bushingwouldworkonthisconstruction. Instead,threepiecesofHK-typeneedlebearingswereused.For thesebearings,themanufacturer givesacoefficientofrollingfrictionof0.003,whichleavesasafetymargin of15forbearingfriction. TheMarmanclampistensionedbytighteningthetensioningscrewwithapre-determined torque(Figure4). Duringdevelopment teststorqueversustensioncurveswerefirstcalculatedandthenexperimentally confirmed. Intests,severalstraingagesweregluedalongtheMarmanclampcircumference andtension wasmonitoredwhiletighteningthescrew. ®Short Shelf Figure4.TopviewofCAPS/ACT. Thetemperature dependency ofthetriggering oftheparaffin (thatmeltsat+80to+100°C) actuator hasin othermechanisms applications beenadrawback because sometimes thetemperature limitshavebeen specified tosuchvaluesthatpyrotechnics aretheonlyacceptable actuators [18].Inspaceinstrument applications, thetemperature limitshavebeenreasonable. Testing Toqualifytheactuator design, anextensive testprogram wasexecuted. Anengineering model(EM)was testedtofullqualification levels.Aseparate lifetimetestingassembly (LTA)wasbuiltinordertoallow testingoflifecriticalcomponents (motor, bearings, position encoder andcablewrap)independently. Prior 258
InCassini mission designs, thethermal analysis ofallhardware wasperformed bytheinstrument system developer. IntheMPRAproject, thethermal analysis isdoneatVTTAutomation. Finding dataaboutthe thermal conductivity ofbearings isaninteresting task. MPRAisthefirstspacecraft mechanism thatVTTAutomation hasdeveloped usingonlytheI-DEAS solid modeler. EarlierdesignwasdoneusingAutoCAD thatallowsfastgeneration ofdrawings butis cumbersome inadesignprocess withamultitude ofdesignchanges. Thetoolhasnotfullybeenusedasa teamtoolsincethemajorpartofthemechanical designhasbeendonebyjusttwoengineers. Unfortunately, theelectrical designisstilltotallyexternal, andeventheintroduction ofwasteheatofthe electronics components toanI-DEAS thermal modelrequires manual operations. TWINS In1999,VTTAutomation startedtobuildtwoscanning actuators oftheCAPS/ACT-type forNASA's TWINS instrument [21].TheCriticalDesignReview ofthisprojectisinFebruary 2000.MPRAandTWINS projects haveledVTTAutomation toasituation whereitsproduct isnotnecessarily uniqueeverytimebutonethat evolves fromanearlierdesign. Thisissensible economically andfortechnical risk.Thisisanoveltyinall Finnish spaceindustry (whose onlyseriesproduction hasbeenhardware for4Clusterand4Cluster II satellites -a"payoff' ofthesadlypoorlaunchvehicleperformance duringthelastdecade). FLATSPRING insideoF'theMPRA) M_INLEVER AUXILIARY LE"_ZR V£AKSPRINGTIGHTENING BOLT VIA Figure5.MPRANPRALOV£R PART 26O
Culturaldifferences areseenoccasionally. TheEuropeans areusedtosolidlubricants andtheAmericans haveavastexperience inliquidlubrication. Liquidlubrication wasusedintheearlyspacemissions thatthe Europeans watched fromtheground. Thusliquidlubrication haslongflightheritage intheUSA.ESAhas invested onsolidlubrication anditisthuspopularinEuropean missions. TWINSPDRreviewpanelstated doubtsonthelifeanddebrisissuesofsolidlubricants. Thefactthatthetemperature difference between theupperandlowerbearinginACTwaslimitedtomax 10°Cinordertokeepthepreloadintherightrangecausedsomethermaldesignconsiderations forTWA.If thetemperature difference wouldbesomething else,anewtestprogram wouldhavetobeexecuted. The problemwassolvedbyathermaldesignusingheatersandthermistors. Conclusions Finlandshouldhavegotteninvolved inspacecraft engineering inthe1970's.Despitethelatestart,V]-I" Automation andtheFinnishspaceindustryingeneralhavegottenatolerable numberofflightreferences andgainedknow-how inthepasttenyears.Forthefirsttime,thereisapossibility todelivernewflight unitsthathaveaFinnishheritage. VTTAutomation's mechanisms experience hasbeenlimitedtosystems thatusesteppermotorsandparaffinactuators astheprimemovers. Thisexperience hasbeenenlarged to planetary drillingandsampleacquisition "robotics" makingthemechanisms sidestronger withinthespace technology group. 262
References t.http://www.kaydon.com, Kaydon, USA. 2.www.aeat-Drodsy_.com/subdivi_ions/ESTL.html, European SpaceTribology Laboratory, UK. 3.FourthEuropean SpaceMechanisms andTribology Symposium, ESA,SP-299. March1990. 4.MIL-A-83577B, Assemblies, movingmechanical, forspaceandlaunchvehicles, General Specification for.USAF,USA.1988. 5.www.launchspace.c0m 6.P.Conley, SpaceVehicleMechanisms, Elements ofSuccessful Design,JohnWiley,1998 7.SpaceMechanisms Standard Requirements Specification, draft02,ESTEC, 1994. 8.www.penny-qil_,-¢0ntrols.co.uk, Penny&Giles,UK. 9.http:llwww.starsys.comlproducts.htm. StarsysResearch Corporation, Boulder, Colorado, USA. 10.Clarence "Kelly"Johnson, MaggieSmith,LeoGeary,Kelly-MoreThanMyShareofIt,Smithsonian Institution Press,1990. 11.HeikkiHuomo,HeikkiHannula, KaiViherkanto, "Periscope Mechanism forSWANInstrument", Proceedings of'FifthEuropean SpaceMechanism andTribology Symposium', ESTEC, Noordwijk, The Netherlands, 28-30October 1992,ESASP-334, April1993. 12.www.novotechnik.de, Novotechnik, Germany. 13.www.snfa.com, SNFA,France. 14.JayAlanMoody,WilliamL.Chapman, F.DavidVanVoorhees, A.TerryBahill,MetricsandCase StudiesforEvaluating Engineering Designs, Prentice HallPTR,NewJersey,1997. 15.http://www.betatronics.com/, Betatronics, Inc.,NewYork,USA 16.Separation Systems Technology Program, PhaseAFinalReport,ESACR(X)3910,SaabEricsson Space,Sweden. 17.RobertDiTolla,MichaelErnst,"Allowable DesignLoadsforMarman ClampSystems", Engineering, Construction andOperation inSpaceIV,Proceedings ofSpace'94,Volume1,ASCE,1994. 18.LowShockSeparation Mechanism, FinalReport,VTTAutomation andRejlers,Finland. 1998. 19.TomiYlikorpi,TimoLuntama, KaiViherkanto, Veli-Pekka Lappalainen, HeikkiHannula, HeikkiHuomo, "Development ofanActuator forCAPSInstrument onSpacecraft Cassini", Proceedings SixthEuropean SpaceMechanisms &Tribology Symposium, Zurich,Switzerland, 4-6October 1995,ESASP-374, August1995. 20.H.Astola, K.Viherkanto, T.Ylikorpi, M.Verain, "MultiPurpose Rotating Actuator forSatellites", Poster presentation at8thEuropean SpaceMechanisms andTribology Symposium, 29September -1October 1999atToulouse, France. 21.http:llnis-www.lanl.gov/nis-projectsltwinsl, TWINShomepage. 263
Coaxial CableFailure inaSpacecraft Mechanism Michael Chiu" Abstract Aftercompleting alifetest,theBiaxialAssembly's (BA)coaxialcablesfailedtheirpost-life RFperformance testing. Further investigation intothecauseofthesefailures revealed thatthecoaxialcablesdeveloped extensive damage totheiroutershields, whichresulted inunacceptable RFperformance. Thisdamage was caused byaphenomenon knownas"coldwelding", atypeofadhesion between twosimilarmaterial fretting surfaces thatrestricted theinternal flexingofthecable. Thispaperwillsummarize thetestingenvironment towhichtheBAwasexposed anddescribe theresultsof ourinvestigation intothefailures. Also,methods ofpreventing coldwelding willbedescribed, aswellas lessons learned forcoaxialcableconstruction andlifetestingofspacecraft mechanisms. Introduction TheBAisequipped withacablewrap assembly, essentially acontrolled service loopconsisting offlexible coaxialcables, anumber ofDCribboncableassemblies, andacoppergroundstrap.Thiscablewrap is dividedintofourchambers. Onepairofchambers iscounter-wrapped withrespect tothesecond pairto provide eventorquedistribution astheoutputshaftrotates. Twoofthefourchambers housecoaxialcables, whicharelooselywoventogether usingapolytetrafluoroethylene (PTFE) tapeandareapproximately 2.13 meters(7feet)longinsidethecablewrap. Essentially, thecablewrap behaves muchlikeaclockspring, withthecablesconstrained astheyenterandexitthecablewrap bytwobridgeclamps (Figure 1).Thetotal travelofthecablewrap isgreaterthan360°. Cable Clamp Figure 1.Cross-sectional viewofthecablewrap assembly "TRWSpaceandTechnology Division, Redondo Beach,CA Proceedings ofthe34_Aerospace Mechanisms Symposium, Goddard SpaceFlightCenter,May10-12,2000 265
Theparticular unitwiththeRFfailures wasanEngineering Qualification Model(EQM). Thus,itwentthrough fullqualification testing, including thermal cycling, random vibration, andthermal vacuum. Beforeandafter everymajorstageoftesting, theRFperformance ofthecoaxcableswasmeasured andfoundtobewithin specification. Aftercompletion oftheseenvironmental tests,theunitunderwent acomplete lifetest.Aswithmanylife tests,thisparticular onewasperformed atanaccelerated ratewhencompared totheactualmission profile. Bydoingso,therequirements of14x106degrees oftraveland7x105directional reversals wasaccomplished inthreemonths instead ofseveral years.Tocomplete boththetravelandreversal requirement atthesame time,theBAwasactuated ina"sawtooth" profile,asseeninFigure2. 240140'o.,... 0 _.= o40 n. ,,9,= "_-60" < -160"m_2880°travel __-_--- 2 4 6 8 10 12 14 16 Time(rains)520° -260 "---P--; 0 18 20 Figure2.LifeTestTravelProfile Thissawtooth profileconsisted ofaseriesof+15°#10 °dithering motions, combined a+120°slew,andwas repeated approximately 5000times.TheBAslewedatitsmaximum operational rateof~3°/sec. Theentire lifetestwasperformed underavacuum of<6.6x103Pa(5xl0-Storr) andatavarietyofoperating temperatures, fromlabambient to~60°C. ii-_---- ±_---!CC NoRFtestingwasperformed dudngthelifetest.Thepost-life RFperformance testrevealed thatallthe coaxialcableswerefailingvoltage standing waveratio(VSWR) 1forfrequencies >5GHz,withincreases as muchas120%fromtheirpre-lifevalues. Also,somehadunacceptable insertion loss2values. The= 1VSWRisonestandard waytoexpress theamount ofreflected energyduetomismatches withinthecable.Foran idealcable,thereisnoenergybeingreflected backtothesource,resulting inaVSWRequalto1.Theequation for VSWRis:V53Xr,R=_l+p,wherep=Reflected Energy l-p Incident Energy 2Insertion lossisanother standard expression involving howmuchenergyistransmitted through thecable.Ideal cablestransmit allincident energy, resulting inaninsertion lossvalueof0.Insertion lossisdefined as: 266
magnitudeoftheinsertionlosschanged asafunction ofoutputshaftposition, withthelargestvalue occurring whenthecableswerefully"unwound" insidetheirrespective chambers. However, thecoaxcables didhaveacceptable performance inbothVSWRandinsertion lossforfrequencies <5GHzforalloutput shaftpositions. Thistypeofcoaxialcableis~0.48cm(0.19inch)indiameter andisusedinhighfrequency, low-loss applications. Thecableconsists offivecomponents: anouterperfiuoroalkoxy (PFA)jacket,asilver-coated flatcopperwirebraid,asilver-coated flatcopperfoil,aPTFEtape-wrapped dielectric core,andastranded silver-coated copperinnerconductor. Dielectric core  \..... • " Stranded Ag-  Ag- "_ olatedCu olatedCuHelically wrapped Ag-plated Cufoil Figure3.Construction ofthecoaxial cableusedintheBA Investigation Investigation intotheseanomalous readings beganwithtimedomain reflectometery (TDR)testing, which provides animpedance versuscablelengthplot.Thesetestswereperformed atanumber ofoutputshaft positions because theinsertion losswasobserved toincrease asmuchas80%depending ontheoutput shaftposition. TDRplotsshowed anumber ofsignificant spikesinimpedance ofthecables, withthe majority ofthespikesoccurring insidethecablewrap neartheinnerhub,atthesmallest bendradius. The magnitude ofthesespikesweredependant onoutputshaftposition (seeFigures 4and5),withthegreatest magnitude corresponding tothehighest insertion lossreadings. Thesehigherinsertion lossreadings occurred whenthecableswereinthefullyunwrapped condition. Thenextstepintheinvestigation wastophysically inspectthecablesthemselves, whichprovedtobemore dramatic. Asthecablewasremoved fromthecablewrap andstraightened out,thecablehadanumber of dents,orkinks.Attheselocations, thewirebraidappeared disturbed, or"birdcaged"asviewedthrough the translucent jacket. Thelargestdamage wasconcentrated withinthefirst0.9meter(3feet)fromtheinner hub,although damage wasobserved asmuchas1.5meters(5feet)away.Also,someoftheouterjacket andshieldhadbeenpunctured, revealing thedielectric underneath (Figure6). Insertion Loss(dB)=-20logVtrans"ittd ,whereVisvoltage Vincident 267
c_Si_ 1in R_F_.0 Units , 20.0nIJnItsl Connector #1r' ms sr_r-_.¢,-_ N'I-I_ _5.0r'm__ IAw, 1ToR,,s0,ke,,r_Ik IS,7_'/' ml. MARKE__ i_,i5n5 Connector #2 ___.._(near hub) _:4_,:399e] Figure4.TDRplotofoneoftheBA'scoaxialcablesintheunwrapped position. IConnector #1P'i_ t_o_,Unit_ J ,I-_i:l,n i [L , • ..lll_ _ m! a STOP_.O_m II] -- - --I,-J  t TDR"spike" ,........ I .........,_..__--ID tJI_.B) t:m _,7112nil A_,7A5 19.A5 Connector #2 (nearhub) 268
ure5.TDR)lotofsamecableinthewra )osition. Figure 6.Photoofthecoaxcableafterremoval fromthecablewrap Thelocation ofthedamage matched thespikesobserved intheTDRmeasurements. Furthermore, when theBAwasactuated, thegapsintheoutershieldstendedtoclosewhenthecablewrap wrapped tighter, explaining thedependence oftheinsertion lossonoutputshaftposition. Physical dissection ofthecablepointed tothecauseofthedamage. Photos usingaScanning Electron Microscope (SEM)revealed thatthewirebraidhadbonded tothefoilshieldatvarious locations (Figures 7& 8). Figure7.SEMphotoofatypical damaged section ofcoaxial cable,withjacketremoved 269
(10xmagnification) Figure 8,SEMphotos ofthecoaxial cableshowthewirebraidandfoilbonded together (200xmagnification) Studyintohowthewirebraidbonded tothefoilpointed toaphenomenon knownas"coldwelding". Cold welding isamolecular-level bonding thatoccurswhentwoatomically clean,smooth surfaces areinintimate contact. Silverisonematerial highlysusceptible tocoldwelding, duetoitshighductility. Coldwelding occursreadilyinavacuum environment duetothelackofoxidation between thetwosurfaces. Asitsname suggests, coldwelding doesnotrequireelevated temperatures tooccur. Therewere3typesofcoldwelding foundinthecoaxcables;foil-foilcoldwelding, foil-braid coldwelding, and braid-braid coldwelding, allinvolving similarmetals(inthiscasesilver)contacting eachother.However, onlyonetypeofcoldwelding, thefoil-to-braid coldwelding, caused thelocalized deformation withinthe cable. Thewirebraidandfoilslideovereachotherasthecableisflexed. Thismotionremoves theexisting silver oxidelayer,providing cleansurfaces forcoldweldstoform.Whenthewirebraidandfoilcoldweldtogether, thisrelative motionisprevented, andahingepointiscreated. Eventually, thecontinued flexingfatiguethe wirebraidandfoil,withtheouter jacketnowkeeping thecabletogether. Inlocations ofthemostflexing, the outerjacketwasalsoobserved tofatigue. Thisfailuremechanism wasproveninsubsequent flexuretestsof isolated cables, asdescribed inthenextsection. Resolution WastheBA,bybeing subjected toalifetestunrepresentative oftheac:tual-mission- profile,overtested ordid thecablesneedtobereplaced? Asmentioned before,thelifeoftheunitwascondensed intoathree-month test,wheretheBAslewedatahigherrateanddifferent motionprofilethantheactualmission. By performing twoflexureteststodetermine howtherateofmotionandamount oftravelaffected coldwelding, theanswertothe_overtest question wasfound.Usingfreshpiecesofcoaxialcableswith thesame construction asthefailingones,theflextestsweresetuptosimulate thecablewrap configuration inthe BA.Thecableswereflexedaroundthesamesizehubasintheca_)elewrapandwerebondedin two restraining fixtures whichkept t_ecablesinplaceyetd[dnotsubjectthemtoanyclamping forces(similar tothecablewrap). Thetestwassetupperthedrawing inFigure9.Allflextestswereperformed ina vacuum ofatleast1.3x102Pa(1.0xl04toE). 270
CCWEXTREME SLEWCWEXTREME CYCLE 10° CCWEXTREME DITHERCYCLECWEXTREME Figure9.Sketch offlextestsetup Another purpose oftheseflextestswastoscreenwaysofpreventing coldwelding incoaxialcables. By identifying howcoldwelding occurs, methods ofpreventing itsoccurrence presented themselves. Onesuch method istoplacesometypeofbarrier, madeofmaterials different thanthewirebraidandfoil,between the twocomponents. PTFEtape,thesametapeusedinthedielectric coreofthecable,wasselected asa goodcandidate duetoitslowcoefficient offriction. Another waytoprevent coldwelding istohavethewire braidandfoilbeofdissimilar materials. Onesuchmaterial proposed forthewirebraidwasacomposite metal/fiber material, providing bothstrength andconductivity. Bothsuchcableconstructions wereflex tested. Theflextestswerebrokenupintotwodifferent tests,bothwithdifferent average velocity ratesanddegrees offlexure. Thefirsttest,hereinreferred toastheslewtest,hadthecablesflexingatanaverage velocity of 6.7°/sec witharangeoftravelof+100°.Thereweresixcablessubjected tothistest:twoPTFE-barriered cables(referred toasPTFE-B cables), twocomposite wirebraid(CWB)cables, andtwocablesoftheold construction. Allthecableswereflexedaminimum of264,000 slewcycles. Thesecond test,referred toasthedither/slew test,flexedthecablesatanaverage velocity of1.7°/sec with acombination of+10°motions (dithers) and_+100°motions (slews). Theseflexingmotions werealternated periodically throughout thetest,whichmorecloselyrepresents theactuallifetest.Atotalofninecables 271
(threeofeachtype)underwent thistestandwereflexedforaminimum of185,000 dithercyclesand20,000 slewcycles. RFtestingconsisted ofVSWR, Insertion Loss,andTDR'stakenatfrequencies between 1-15GHzat various intervals throughout bothtests.Allcableswereterminated withSMAconnectors atbothends, similartotheBA.TheRFtestingwasperformed whenthecableswereinthefullunwrapped configuration (CWextreme, seeFigure9),thesameposition astheworstRFresultsfromtheBAtesting. Results SlewTest Fairlyearlyintothetest(-500cycles), theoldcablesexhibited signsofcoldwelding thataffected RF performance. TDRtracesshowed spikes,indicating damage tothecables, atlocations wherethecables wereseeingthemostflexure, -1cmfromtheclamps. Visualexamination confirmed thepresence ofcold welding ofthebraidtothefoil,asindicated bythedistortion ofthewirebraid.Eventually, theouterjacket separated intwoplacesononecable. RFperformance oftheoldcablesremained inspecification inthelowfrequency rangeof<5GHz.However, inthefrequencies >5GHz,alltheoldcablessawincreases intheirVSWRandInsertion Lossresulting in outofspecification conditions, whichoccurred starting at-120,000 cycles. Although thePTFE-B andCWBcablesdidexperience coldwelding ofthefoilwithitself,neitherdeveloped thecoldwelding between thebraidandthefoilthatdamaged theoldcable.TDRtracesremained similar throughout thetest,andRFperformance stayedwithinspecification. Tables1and2summarize theworstcaseRFperformance ofthecablesintheslewtestatvarious frequencies. Eachnumber represents themaximum orminimum valuemeasured throughout theentiretest, alongwiththeexpected valueforthistypeofcable. Table1:RFPerformance at-2GHzRangeforslewtest CableType NominalMaxVSWR MinInsertion Loss(dB) 1.2 -0.412 Old 1.19 -0.39 PTFE-B 1.10 -0.34 CWB t.11 -0.38 Table2:RFPerformance at-15GHzRangeforslewtest MaxVSWR 1.35 Old 1.92 -3.74 PTFE-B 1.26 -0.91 CWB 1.24 -1.07CableType NominalMinInsertion Loss(dB) -1.08 Dither/Slew Test Thedither/slew testbeganwiththecablesdithering forapproximately 47,000cycles,duringwhichthe cablesexhibited nochange inRFperformance orintheirTDRprofiles. However, oncethecablesunderwent slewcycles,theoTclc, ab]esd-evel0ped spikesintheTDRtracesandth_eirwirebraidsdistorted inanumber ofplaces. Eventually, alltheoldcablesdeveloped cracksintheirouterjackets, asseeninFigure10. 272
+ Figure 10.Picture oftheoldcablesafterremoval fromdither/slew test showsouterjacketsplitting. Theoldcableseventually wentoutofspecinthehigherfrequency rangesstarting at94,000totalcycles (87,000 dithers, 7000slews). TheRFperformance atthelowerfrequency rangeneverwentoutofspec.As forthePTFE-B andCWBcablesthatunderwent thedithedslew test,theirRFperformances andTDRtraces remained stablethroughout. Tables3and4summarize theRFperformance dataforthedither/slew test. Table3:RFPerformance at-2GHzRangeforDither/slew Test CableType Nominal Old PTFE-B CWBMaxVSWR MinInsertion Loss(dB) 1.2 -0.412 1.11 -0.36 1.08 -0.39 1.10 -0.40 Table4:RFPerformance at-15GHzRangeforDither/slew Test CableType MaxVSWR Nominal Old PTFE-B CWBMinInsertion Loss(dB) 1.35 -1.08 1.88 -4.04 1.15 -1.07 1.13 -1.2 273