ai-aerospace/ams_data_full_2000-2020 huggingface dataset:
Resul ts 

The torq ue was ob served to be extrem ely stable for ty pically more than 90% of the life for each pai r of  beari ngs. As an example, the torqu e trace of a Penn zane-lubricated bea ring ju st after being  installed into   the fixture (Fi gure 4) is nearly identi cal to the tra ce measured aft er 453 millio n cycle s (Figu re 5). Note th e  transitio n from the con stant test oscill ation to the constant rotation pattern u sed only durin g health ch ecks. 

Figure 4.  Pennza ne 2001 Bearing Tor que Trac e at 0 c ycles 

Figure 5.  Pennza ne 2001 Bearing Tor que Trac e at 453M c ycles 

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There are two indi  torque sig nature. 

Figure 6.  Pennza ne bea ring torqu e trace appr oaching failure. Note torq ue spike   cators of lubricant de gradation o bservable i n a beari ng health che ck The first, and  more n oticeable, is the d evelopment of  torque bump s during th e tran sition fro m oscillation s  to co ntinuou s rotation  (Figure 6). T his is an early in dicator of lu bricant breakdown for bearings operating   in a gimbalin g motion. De bris mo unds form at the end of each st roke as the b ack and forth  motion over  one spot on the bea ring race continu ously stresses the lubri cant without the a bility to bring “fre sh” oil into   conta ct. The result is small amount s of lu bricant bei ng degrade d into  a slud ge-like friction poly mer (Figu re  7). Eventually  this lead s to torque bump s, when the stroke i s increased. Subse quent roll-ove rs cause the  balls to  break throug h this buildup, which h elps smooth out th e torque. B earing failu re is considered to  occur when the torqu e reaches thre e to four times th e starting steady state tor que. The oth er indi cator of  beari ng de gradation i s increased ave rage torque a nd torque ha sh (high fre quency noise) during th e  constant rotat ion portio n of the torque te st. This o ccurs in a later st age of lubri cant degra datio n. Note the   marked change in torqu e signature between Figu res 5 and 6 in just 20 million cy cles (5% life).  Torque  Spike  of > 1 in-lb fr om debris bump at tra nsition to 3 rev s of con tinuous rotation  

Figure 7.  T ypical Bearin  Lubricant, Post-Failure  g 338
Summary of Results   esults are summa rized in Tabl e 2. These results sh ow th at bearin gs lu bricate d with  he introduction of TiC-co ated ball s showed no stat istical significant life improvement rel ative to the   s shown in Figure 8, the three enviro nmental-fri endly cleani ng solvents pe rformed g enerally better tha n  Table 2.  Summar y of Results – Beari ng Life, Milli on C ycles  LubricantThe cumulati ve test r Pennzane  2001 oil h ad th e longe st life.  It is cl early superio r to th e other l ubricants, indep endent of solve nt  cleaner. Ave rage life  was extended  by a facto r of approxim ately 9X wh en compared to  those bearings  lubricated with Brayco 81 5Z. The results al so show that Kryto x 143AB offered no life improvem ent  relative to Brayco 81 5Z. The silahyd rocarbon lubri cant extended a verage life by  2.8X. A similar ra nking of   lubricants was obtaine d using a Va cuum Spiral O rbit Trib omete r [7] where a silahydro carbon relative   lifetime wa s much  greater than B rayco  815 Z or Krytox 143AC l ubricants but clearly n ot as good as  Pennzane 2 001.  

T stand ard 4 40C stainle ss steel balls for the Pennzan e-lubricated beari ngs (not e that one of the TiC test  beari ngs is sti ll under te st, curre ntly at 386 million cy cles). Simila r result s were found by Jan sen et. al [8].  

A Freon 11 3. Hepta ne was use d to re-clea n the b earings prior to lubri cating with the silahydro carbon  lubricant. It al so showed perform ance as good or better tha n Freon 113. Th e variation s in lif e are mainly   due to the test lubrica nt. 

 2SR = Still Runnin g Brayco 815Z Krytox 143AB Pennz ane 2001Pennzane  TiC BallsSilahy drocarbon Freon - 113 10.1 9.0 265.5 - - Freon - 113 12.6 40.0 118.5 - - Brulin 815G D 15.0 30.2 481.5 385.8 SR2Brulin 815G D 35.6 60.0 165.8 141.0 - 3M PF -5052 40.5 29.4 409.0 - - 3M PF -5052 33.1 - 372.0 - - DuPont Ver trel XF 26.1 - 360.0 - - DuPont Ver trel XF 108.2 - 349.0 - - Heptane - - - - 131.0 Heptane - - - - 110.9 Heptane - - - - 62.8 Averag e Life 35.2 33.7 315.2 263.4 101.6 Ave. Life Factor 1.0 1.0 9.0 7.5 2.9 L10 Life 7.3 8.2 131.0 - 47.0 L10 Life Factor 1.0 1.1 17.9 - 6.4Solvent 339
0100200300400500 Freon -113 Brulin 815GD 3M PF-5052 DuPont Vertrel XFHeptaneLife, million cyclesBrayco 815Z Krytox 143AB Pennzane 2001 Silahydrocarbon Figure 8.  Effect o f Cleani ng Solv ent on Av erage Bearing Life 

Weib ull analy sis was perfo rmed o n the test beari ngs to show the effects of reli ability on measu red life,  Figure 9. The  L10 lives (90% reliability) of the four te st lubri cants are shown in Figure 9. At the L10 l evel  the life advan tage of Penn zane 2001 relative to Brayco  815Z o r Krytox 143AB is ap proximat ely 16 to 18   fold (see Ta ble 2). The silahydro carbon-lubricated bearin gs enjoy ed ab out a 6 X life advantage at 90%   reliability. 

Bearin gs lubricated  with t he fou r test oils exhi bited  similar failure dist ributions, i.e., Weib ull slop e. Life   differen ces betwee n Krytox 143AB and Brayco 8 15Z lubricated b earings are not  statistically si gnifica nt. 

Figure 9.  Weibull Analy sis of Be aring Life 

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The life results presented  above  were  affected  by beari ng te st accele ration  factors as noted. These  factors in clude highe r than  normal p reloads, le ss lubricant than n ormal, and ne arly contin uous dithe r over  the same spot on th e raceway. Flig ht beari ng life  under le ss severe condition s may actually be g reater  than that rep orted in this study. 

Conclu sions  

The seve n-year bea ring life test prog ram supp orts the followin g conclusions:  1. Pennzane 20 01 lubricated beari ngs provided a 9X av erage life imp rovement relative to either the  Brayco 8 15Z or Krytox 143 AB lubricate d bearin gs. The L10 life imp roveme nt was 16 to 18 tim es. 

2. Krytox 143AB sho wed comparable life to t he baseli ne Brayco 8 15Z lubricated b earings. 

3. A silahyd rocarbon lubricant  produced an L10 bearing life that wa s about 6X g reater tha n that with  Brayco 8 15Z or Krytox 143 AB. 

4. TiC-co ated b alls di d not offer a life a dvantage over 440C stai nless steel  balls for the Pe nnzane  2001 lu bricated bea rings. 

Referen ces 

1.    Loewenth al, S.H., Jone s, W.R. Jr., G rout, J ., Pre dmore, R.E., and Th om, R.,  “Instrume nt Bearin g  Life With  Non-CF C Cleaners”, DOD Rolli ng Be aring  Workin g Group  & C.S. Drape r Lab s,  Proceedi ngs of the Interna tional Rollin g Elem ent Bearing Sym posium, April, 1997. 

2. Loewenth al, S.H., Jone s, W.R. Jr., and Predmo re, R. E., “Life of Pe nnzane a nd 815Z-Lub ricated  Instrum ent Bearin gs Cleaned With Non-CFC Solvent s”, Proceedings of the 8th Europ ean Sp ace  Mech anisms and Tri bology Sym posium , ESA SP-438, September, 1999. 

3. Jones, W. R., Jr, Tod dy, T.J., Predmore, R., Shogrin, B., and Herre ra-Fierro, P., “The Effect of   ODC-F ree Cleanin g Techn iques on Bea ring Lifetime s in the Parch ed Elastohyd rodynami c Regime”,  NASA TM 107322, August , 1996. 

4. Jansen, M.J., Jone s, W.R.,  Jr., Whe eler, D.R., and Ke ller, D.J., “Evaluation of Non-O zoneDepleting-Ch emical Cleaning Method s for Spa ce Me chanisms Using a Vacu um Spiral Orbit Rolling  Contact Tribometer”, NASA TM-2000-210050,  May, 2000. 

5. Gsch wender, L.J., Snyder, C.E., Jr., Massey, M., and Peterang elo, S., “Improved Liquid/G rease  Lubri cants for Space Me chanism s”, Lubr. Eng ., 12, 56, pp 25-31 (2000). 

6. Jones, W. R. Jr., Ja nsen, M.J., Gschwe nder, L. J., Snyder, C.E. Jr., Sharma, S.K., Predmore, R.E.,  and Dube, M.J., “The Tri bological Prope rties of Severa l Silahydro carbon s for Use in Space  Mech anisms”, Procee dings of the Ninth Europ ean Sp ace Me chansims and T ribology Symposi um.,  SP-480, Sept embe r, 2001.  

7. Jansen, M.J., Jone s, W.R. Jr., Predm ore, R.E., and Loewe nthal, S.H., “Relative Lifetimes of  Several Space Liquid Lubri cants Using a Vacuum Spiral Orbit Tri bometer (SOT)”, NASA TM 20012109 66, Ju ne, 2001. 

8. Jansen, M.J., Jone s, W.R. Jr., Peppe r, S.V., Wheeler, D.R., Schröe r, A., Flühman n, F.,  Loewenth al, S.H., Shogrin , B.A., “The Effect of  TiC-Coated Balls a nd Stress on the Lubri cant  Lifetime of a Synthetic Hydro carbon (Pennzane 2001A) Using a Vacuu m Spiral Orbit Tri bometer”,  NASA TM-2000-210525,  October, 2000.   341
(M/E assemb ly), suppo rted by a dupl ex pair set of thin se ction an gular conta ct bearin gs (see Figures 1 &  4). The M/E duplex pai r (DB) be aring is mad e up of  an “A” be aring and “B” b earin g. The i nner, a nd out er  spacers, races, an d balls were m anufa ctured with passivated, CEVM 440 C Stainless Steel . The b earing  confo rmity ra tio is 52.5% (race radius / ball di ameter). The races and 88 ball s per bearing were treated  with Tri cresyl Phosph ate (TCP) for 7 2 hours at 107 °C (22 5°F) per federal spe cificatio n (TT -T-656). Each  beari ng was lubricated with app roximat ely 240 millig rams of Bray  815Z oil i n Novemb er 1981 by Split  Ballbea ring. Both spa cers were grea se plated with Braycote 3L-38-RP, a teflon thicke ned grea se using  Brayco 815 Z base oil. The bearing se parators are Teflon toroid s around altern ate ball s. Through out this  pape r, refere nces will b e made to the two sets of be aring s for e ach FGS Servo in the followin g manne r: 

FGS Servo  Motor/Encoder Bearing Assy . Bearing Pair  A 3009 007 0-107 A & B  B 3010 008 0-106 A & B 

Previou s engineeri ng fin dings by Stu L oewenthal  et al[2] from  ground -based life tests ide ntified that a  build-up of d egraded lu bricant from ex cessive CT cycling cau sed a “bum p” for the ball to roll o ver pri or to  contin uing to its requi red p osition (Figu re 2).  This bu mp cau sed a spi ke in the motor voltage  as indicate d  by the Comp ensated Error (CE) si gnal, which is a di rect indication of a high torq ue. This CT torqu e bump,  occurrin g at nominal 9.8 degree ball defect spa cing, has bee n observed to some extent on all FGS  beari ngs, but prima rily on A servo s due to the meth od for sampling the CE si gnal. Ho weve r, the pri ncipal  reason for refurbi shing FGS-1 was due to servo -B repe atedly  stalling after directio n reversal  during  vehicle offset  slews (Fig ure 3). Unlike CT bump s, the exact cau se of this “rev ersal” bu mp (RB) re maine d  unkno wn alth ough  believe d to b e a distinctly differe nt type of b earing anomaly, possibly related to i nternal  or foreign d ebris. O nly FG S -1B and -3B exhibited this  problem, with FGS-3B in  an early stage. However,  FGS-3B is still in operatio n. 

Figure 1.  SSS Motor/Encoder assem bly (Top). HS T FGS-1 SSS-B after cov er remo val (Bottom) [3] 

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FGS SERVO  1A MAX CO MP ERRO R DURING VEHICLE OFFSET  MANEUVERS 01234567891011 1991 1992 1993 1994 1995 1996 1997 FGS SERVO 1B CO MP ERRO R DURING VEHICL E OFFSET  MANE UVERS 01234567891011 1991 1992 1993 1994 1995 1996 1997FGS SER VO 1 A FINE LOCK MAX COMP ERROR 012345678910 1991 1992 1993 1994 1995 1996 1997 FGS SERVO 1B FI NE LOC K MAX COMP ERROR 012345678910 1991 1992 1993 1994 1995 1996 1997FGS SERVO  1A MAX CO MP ERRO R DURING VEHICLE OFFSET  MANEUVERS 01234567891011 1991 1992 1993 1994 1995 1996 1997 FGS SERVO 1B CO MP ERRO R DURING VEHICL E OFFSET  MANE UVERS 01234567891011 1991 1992 1993 1994 1995 1996 1997FGS SER VO 1 A FINE LOCK MAX COMP ERROR 012345678910 1991 1992 1993 1994 1995 1996 1997 FGS SERVO 1B FI NE LOC K MAX COMP ERROR 012345678910 1991 1992 1993 1994 1995 1996 1997

Figure 2. Max Compe nsated Erro r (CE ) during vehicle offset m aneuv ers s howing CT bumps  (Left), and d uring Fine L ock sh owing Rev ersal Bumps (Right).  No te: motor stall ca n  occur ab ove 10V Comp Error. 

Vehicle Offset Slew Vehicle Offset  SlewRate Reversal SlewReversal Bump CT Bump

Figure 3. Example of FGS-1 SSS-B Rev ersal Bump. In itial direction of motion is right to left.    Note CT bu mp at end o f CT stroke (bar, uppe r panel).  Direc tion rev erses at a position  of abou t -4,7 00 arcs econ ds and a 6.1-v olt Rev ersal Bump form s. [2] 

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(2) (2)  16.5 cm  Bearing  Bore 

Figure 4. FGS-1 Motor/Encoder SSS-A bearing assy.  Encoder optical di sk sho wn (white  particula te identifie d by white arr ows) (Le ft).  Clamp Ring remov ed and 0107B be aring  expos ed for inspec tion (Right). [1] 

Inspec tion Planning & Te chnolog y  The objec tive of the dis assembly and ins pection of the SSS ass emblies  were t o verify the cause of the  CT b ump a nomaly, but eve n more imp ortantly, determ ine the cause of the reve rsal bum p anomaly sin ce it  was felt that ground testin g well characterize d the CT anomaly b ut could n ever accu rately  explain the   cause of the reversal bumps. After return of the F GS instrument from  SM2 to the HST test facility at  GSFC, several groun d tests were  performed at the i nstrument assembly l evel in an attempt to rep roduce  the on -orbit a nomalie s. The CT b umps encounte red were simila r to that on-orbi t, although  much smalle r  in mag nitude.  Reve rsal Bu mps were  much smaller th an tho se observed  on-orbit (4.4V m aximum vs. 10V  saturation ). By the third d ay of testing, the Reve rsal Bumps disap peared a nd the CT  bum ps were  less  than 2V pea k. 

At the compl etion of instru ment level testing, the M/E’s we re re moved and sent to their manufacturer fo r  addition al testing and tea r down to the b earin g assembly level. Once the moto rs and e ncode r electroni cs  were remove d, the units were sent to the Mate rial Analysis La boratory at L ockhee d Ma rtin for detaile d  inspectio n. The inspe ction/operatio ns flow is o utlined  in Figure 5. 

The process of planning  and creatin g the pro cedure for the  inspe ction was critical to having a   comp rehensive flow that provided the b est ch ance for re solving th e anomaly ca uses. A good  plan re sults  in the most efficient use of time during th e insp ection and test process wh en su pport pe rsonnel are at the   peak and critical eq uipme nt must be sch edule d around other ta sks.   

The first step was to d etermine th e mo st pro bable  causes of the  anomalie s from the availab le data.  This  provide s a focus on the ta sk, b ut shoul d not limit th e ability to sh ift focus onto other areas of con cern or  potential causes. Con clusions shoul d not be drawn here, but allow for a wid e range of probable and likely  reasons for t he anom aly. All relevant d rawings, test  and flight dat a sho uld be collected a nd reviewe d in  support of the se hypoth eses.  346
differen ce in locatio n of the degra ded lu bricant on t he toroid (fa ces of 0106 an d bore / OD of 0107) wit h  its observed motion during reversal provides a hypothesis of increased friction between the toroid and  race land. Th e more d egraded lub ricant con dition in the 010 7 bea rings i s consistent with the observatio n  that all of th e A-side  servos g enerally have  more serious CT bump problems than the B-side servos.  Figure 6 is ph otogra phs of the 010 7 and 0106 b earings and lu bricant degra datio n prod ucts. 

Table 1.  Star Selector Se rvo Subs ystem Performa nce Tes t Data Comparis on [3] 

Bearing Inner RaceTeflon Toroid Separator Degrad ed Lu bricantBearing O uter Race Reta iner

Figure 6. Bearin g 0107B (SSS-A) mounted in bearing assembly  housing (Left).  Bearing 0106A  (SSS-B), balls and toroid s after beari ng di sassembly  (Right).  Note locatio ns of  degrad ed lubricant on the separ ator. [1]  350
There i s no concl usive eviden ce that th e forei gn debris found in the FGS -1 bearing s contributed to th e  probl ems observe d on-orbit. It is surp rising that tor que spi kes were not mo re prevalent du ring on -orbit  servi ce and durin g post-flight testing, con sidering the abun dance of metallic and fibro us debris in bot h  sets of b earings. It i s unlikely that this de bris was introduced duri ng the inspection process, be cause strict  attention was paid to contamination control d uring inspectio n. Also n oteworth y are the observatio n of  variety of co ntaminant s with ma ny types not eve n present in  the in spection a rea, a nd less debris  observed i n the entry zone areas (such as th e hou sing,  clamp rings, et c.) as comp ared to that within th e  beari ngs. The presen ce of flattened fib ers an d metallic p articles, and th e exte nsive denting  on th e balls  and races (po tentially som e of these in flicted by the d ebris) al so indicate these are not a rtifacts introd uced   durin g disassembly. Although some of the alumi num parti cles could conceivably have b een introdu ced  from the alu minum motio n tester, the  flattened, pl ate-like app earance of th e particl es sugge sts that  considerable torque would have bee n required. Fu rtherm ore, the energy req uired to roll ove r this de bris  would undo ubtedly have caused han g-up of  the motor. This sugg ests that the bulk of this d amage li kely  occurre d during ea rly be aring run-ins prio r to fi nal instrume nt assembly. The follo wing parag raphs  descri be the data achieve d from ea ch of the analytical techni ques describ ed in this pap er. 

Figure 7 sh ows the fibe rs from the 01 06B bea ring. Table 2 li sts the fiber size distrib utions from ea ch of  the four be arings. Mo st ob vious from th e table is  that the 0106B beari ng flush  has a g reater numb er of  fibers in each size-ra nge class. Also, th ere were more fibers o bserved in th e "B" beari ngs than in the "A"  beari ngs. The enti re filter surfa ce was scann ed at 50x ma gnification. As sho wn, a l arge number of fib ers  (>60 on e ach filter) we re counted in the  bearin g-flush debri s. To characterize, 8 to 9 fibers of different  types were selecte d for infrared analysis. Th e infrared spe ctra show that the fibers f rom each of t he  beari ngs are predomin ately polyeste r and cellulo sic based compounds. Severa l polyamide -based fibers  (nylon 6 or 66 in some  cases) and an acryli c fibe r were al so observe d. Figu re 8 shows the asso ciate d  FTIR analy sis for a particul ar fiber from this be aring. 

M/E 3010,  Beari ng 0106B, Bl ue (left) and brown  (right)  fibers found  ontoroidprior to flushing. F TIR  indic ated blue to be cellulos ic, and b rown to be  polyamid e. M/E 3010,  Beari ng 0106B, Bl ue (left) and brown  (right)  fibers found  ontoroidprior to flushing. F TIR  indic ated blue to be cellulos ic, and b rown to be  polyamid e. 

Figure 7.  Be aring 0106 B fibers remov ed from filter  paper debri s and analy zed by FTIR. [1] 

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Table 2.  Fiber Size Dis tribution [1]  Size Range,   microns 0106 A  Coun ts 0106 B  Coun ts 0107 A  Coun ts 0107 B  Coun ts  100-250 12 20 8 18  251-500 22 53 24 37  501-100 0 23 47 20 34  >1000 10 28 13 11  Totals 67 148 65 100 

Figure 8. FTIR spe ctra of n ylon libr ary ref. (bottom) and fibe r found in 01 06B be aring (top). [1] 

The bea ring races, ball s, and toroi ds were examin ed prio r to additional cl eaning usi ng an Optical Lig ht  Microsco pe (OLM). T he in ner races and ball s were also examine d using Scan ning Ele ctron Microsco py  (SEM). In both cases, too  much resi dual lubri cant was ob serve d, that masked the we ar or dama ge  evaluation. Hence, the inn er race s and balls were further cleaned using F reon and a polyester swa b  and/or wiper to rem ove th e resi dual lubricant. Due to the size limitation of th e SEM chamber, only the   inner races could be introd uced into the SEM and examined; oute r races were not examined.  

Four balls per bearing were examine d using SE M. The d amage o n the balls was similar to th ose  observed o n the races, e xcept sm aller, typically  less than 20 mi crometers.  Multi-fragm ent dents a nd  pits/pullo uts were n oted in  at lea st one  of the four balls from  each beari ng. Th e most p revale nt dama ge in  the ball track of the inn er races, as observed using SEM, wa s ind ents. The  indents typically range d in size  from 2 0-100 micromete rs in diam eter, a few were less than  20 micrometers. S ome b earing inner races  had in dent patterns th at we re repeated on the same race which suggeste d that d ebris was abl e to cli ng to  a ball o r toroi d as it rolled on the race. The F ringe, d efined a s plastically d eformed metal at the edg e of a  pit or i ndent  that re sulte d from exca vated or  plowed materi al, may be capable of cau sing repeate d  bumpin g during service, h ence, the damage was categori zed as with or witho ut fringe. Fig ure 9 ill ustrates  two example s of a damag e fringe. One  that has bee n rolled ove r durin g service operation a nd one that  has not. 

352
Flush ed pa rticle s that app eared metallic were also analyzed by SEM / EDS to dete rmine their o rigin.  Figure 10 i s an exampl e of a 300 seri es stai nless steel  particle with a sm ooth surfa ce. These su rface  characteristics indicate that the pa rticle was mo st likely in the  bearing  racewa y at so me point and  rolled   over by the balls du ring o peration. Th e origin of th is particl e is p robably from th e mech anism fastene rs. 

Figure 9. SEM photom icrograph o f bearing 01 07B indent without  plastic deforma tion or withou t  edge fring e (Left) and SE M photomicr ograph o f bearing 0106 A with multi-fr agment  indent with plastic de formation or fri nge (Right). [1] 

Bear ing 0107B , SEM  micrograph (l eft) and co rrespondi ng EDS spectr um (right) of th ick  metallic particle, approximately 375 m icrometers in length. EDS sp ectrum indicated Fe,  Cr, Ni, andZr, probably a 300-series stainless steel. Part icle was thick en ough to block  filter paper Ag signal. Bear ing 0107B , SEM  micrograph (l eft) and co rrespondi ng EDS spectr um (right) of th ick  metallic particle, approximately 375 m icrometers in length. EDS sp ectrum indicated Fe,  Cr, Ni, andZr, probably a 300-series stainless steel. Part icle was thick en ough to block  filter paper Ag signal.  Figure 10.  Bearing 010 7B SEM of pa rticle. [1] 

ESCA (Electron Spect roscopy for Che mical Analysi s) was u sed to examine the surfa ce chemistry, and in  particula r to unde rstand the p resence of pho sphorus reaction compou nds (originatin g fro m TCP) and   fluorine  reaction comp ounds (from l ube), if any. One  ball per bearing was exami ned u sing ES CA. Tabl e 3  summ arizes the co mposition of the various b all surfaces after th e initial Freo n flush a nd after furthe r  flushin g. The  dete ction of ionic fluori ne o n the ball surfa ces suggests l ubricant breakdown a nd  subsequent reactio n with the metal(s) in the steel  ball. The p ersiste nce of fluorin e after f lushes and  353
Ackn owledgement 

The autho rs would like to  ackn owledge the i nvalua ble contri butions for the suppo rt an d state-of-th e-art  method s used by the Lo ckheed M artin Material s and Failu re Analysis Te am an d in pa rticula r Dr. A. Jo shi  who o rganized the lab wo rk. 

Referen ces 

1. Joshi, A., Chris tensen, P., J urta, R., Loewenthal, S., & Pellic ciotti, J ., HST FGS-1 Star Selec tor Serv o  Bearin g Insp ection,  LMSS C/P5050 33, 4  September 1 998.  2. Loewenth al, S., Esper, J., Pan, J ., & Decker, J., Space Tel escope Fin e Guidance Sen sor Bearin g  Anom aly, 30th Aerospace Mechani sms Symposium,  NASA CP 3328, pp13-29, May 1996.  3. BEI Sensors & Systems Co., Prelim inary Eval uation Re port for the As-Recei ved Co ndition of  Motor/En coders S/N ’s 3009 & 3010 and  Rem ote Units S/N ’s 4009 & 4010 Retu rned from  the Hub ble  Space T elescope ’s Fine Guidan ce Sen sor / Radial Ba y Modul e S/N 2002, 2 July 1998.  4. Todd, M.J., E uropean Space T ribology Laboratory, UKAEA,  Risely, England, Investigation of Torque  Anom aly in O scillating PDM Bearing s, ESA (ESTL) 49, May 1981. 

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