- like, ” lubri cant with the d egraded l ubricant ad hered to the races and toroid s. There wa s a slight oil fil m  noted around the b alls wh en vie wed under micro scope at ~6x. Hundreds of skin particle s and fibe rs were   found i n bearing flush  filters.  Many metallic particles were also found  on the be aring flu sh filte r and  analyzed by SEM/EDS. Most pa rticle s were dete rmined to be 300 - serie s stainle ss steel,  galvanized  steel, ca rbon steel, 6000  - serie s aluminum and brass. SEM results on th e beari ng ra ces reveal ed  damag e (recorde d only if in wear tra ck) cha racteristics of in denta tions with fri nges, i ndentations with out  fringe s, multi-fragme nt den ts with frin ges, multi-fr agment dent s without frin ges, rep eated dent pattern s,  pits / pullouts and multi-fra gment dent s on the ball s, and dete ction of ionic fluorine on ball surface tha t  suggests lubricant bre akdown. It was al so ob serve d during the bearing rotation tes t that the toroids  tend  to wobble fro m inner to ou ter ra ce wh en the bearin g reverses di rection an d at least one toroid in beari ng  0-106A app eared to skip a cross the ra ce land a s the beari ng rotated. 

There is no conclusive e vidence that the foreign p article s alo ne contrib uted to the on-o rbit anomalie s.  There were  no torque spikes during initial build and t est. The po st flight torqu e trace s were mostly clean,  althoug h not unexpe cted, t he torque noise on the tra ces was about 30% larger, prob ably du e to lack of   lubricant, con tamination, a nd dam age t o balls and ra ceways ove r life.  The FGS life test beari ngs showed  CT bu mps without co ntamination - only degra ded l ubricant. Th e presence of nume rous flat fibers and  metal pa rticles in the bearing and smooth torque  trac es show that the be aring run-in and fun ctional  testing flatte ned th e particles and permitted sm ooth pe rforman ce. All FGS beari ngs yielded smooth  torque  traces initially eve n thou gh th ey most li kely contai n pa rticle s. Deg raded  lubricant wa s most  signifi cant co ntributo r to an on-o rbit Co arse Tra ck torque in crease. Degradatio n debri s collected at the   end of e ach stroke caused a bu mp fo r the b all to roll ove r. Thi s was evide nt from the CT a nomaly  reproduced i n life tests at  Lockhe ed M artin Spa ce Systems Company (L MSSC) in 1 994[2]. Operatio nal  changes in 1 994 si gnifican tly reduce d CT cycle s.  

Reversal  Bumps were never reprodu ced du ring life testing at LM SSC in 1 994 and ground tests on FGS-1  at the GSFC VEST facility,  post SM2, were never able to reproduce the magnitu de of RB’ s seen on orbit.   After three da ys of tests, the existing RB’ s disapp eared. There was inco nclusive eviden ce fro m inspe ction  to explain reversal  bum p phen omen a; however a  hypothes es is that a co mbination of d egraded oil, d ry  beari ng, p articulate  debris and  blocking cau sed th e Reversal Bumps. Reversal b ump characteristics  occurred at ~0.128 degrees (460 arcsec.) after reversal, sugg esting a very steep  torq ue slope. Thi s  indicates that  a foreign particle m ay be caught b etween the ball and  race upon reversing direction. As the  ball rotate s in one dire ction, the toroid edge a cts as a wiper p ushing a pa rticle along the surface of the  ball. When  directio n is reversed, thi s particle  stays with the  ball and gets we dged  between the ball and  raceway crea ting the RB. Also, an erro r or mi salign ment in the ri ng ca n cause the ball to spin a nd the   conta ct angle to fluctuate as it travel s around the bearin g. The chang e in con tact angl e causes varyin g  ball sp eeds that result in the ball s apply ing load to ea ch othe r (Blocking[4]), leadi ng to increa sed torqu e.  As a result of  this in spection exe rcise, several reco mmend ation s were made f or the rebuild  of the future   FGS M/E’s. These in cluded b earing race conformi ty chan ges to redu ce the ball spin, redu cing the  likeliho od of blockin g and simila r oscillatory torq ue anomalie s. Ve rification of adequate  application of  antiwear additive co ating s where  a control sa mple fr om the treat ment may b e required to  validate the   adeq uacy of the process. Strict contam ination control re quireme nts for proce ssing and handling of the  beari ngs and beari ng assemblies. Fin ally, addition of more lu bricant to the bearin gs. 

The meth ods and te chnology utilized fo r this in spection are not u nique to thi s system a nd can be ad apted   to most inve stigations at v arying stage s of the me chanism life fro m developm ent, through te sting, to po st  flight evaluation. The syst ematic  methods used for the HST FGS SSS and specific findings are the  importa nt su bject s of this pape r. The  lesson s learned fro m the hard ware include the im portan ce of  cleanline ss and handlin g for precision instrument bearings and the pote ntial ef fects f rom contamination.   The analytical techniques used fo r the SSS inspection and their i mportance in this investigation should be  considered as  a template for future anomaly s tudies . 

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