The moto r subsequ ently passe d its st anda rd fun ctional test, in both clo ckwise and coun terclo ckwise  direction s, with no anomal ies in its ope ration. Althou gh this stall failure was recovered thro ugh software  operation s that could b e accompli shed on orbit, the test seq uence was discontin ued a nd the moto r  remove d from the life-test  chamb er for disassembly and in spection. 

Inspe ction of the bea rings sho wed th at the lubri cant was in good condition. Ho wever, several small   metallic p articles (as in Fi gure 13) were found in o ne of the two bea rings in the assembl y. Chemical  analysi s reve aled that the particle s were 606 1 series alumi num with trace s of chro mate from irri dite.  Chemi cal analysis al so revealed that  the bearin g lubricant was not othe rwise co ntami nated by the  stainle ss stee l used i n both the ball s and ra ces of t he bea ring. This sugg ested that there h ad bee n littl e  signifi cant we ar to the bea ring ra ces or b alls. 

The hou sing desi gn of the life-test motor was examin ed to dete rmine the  source of the  particles that were  found in  the beari ng and l ubricant. It was concluded that the p robable source was the i rridited, thre aded  holes in the motor’ s alumi num ho using, close to the contami nated  beari ng. Inspectio n of the se fast eners  (in pla ce in Figure 13A) revealed that t he screws’ locking featu res dam aged the thre ads in the hou sing  and pu shed the re sulting debri s into th e motor’ s rot or cavity. The previou s vibration te sting and othe r  handli ng brought the  particles into conta ct with  the bearing where they could  be captu red by the lu bricant.  With time, th e particles caused the stall wh en one or more particles became lodge d between the  balls  and the  races. When th e motor was comman ded t o move in the opp osite directio n, the p article s were  moved o ut of the way or crushed  (expl aining the  observed “stuttering” behavior), and  the m otor be gan to  operate as b efore. 

The key corrective a ction for this anom aly wa s to a dd  an inte rmediate cleaning step to  the HCM  assembly  procedure that remove s the free p articles that we re  gene rated d uring a ssembl y. 

The HCM was re -built  to flight spe cification s with  an  identical bea ring an d se cond life-test serie s was  initiated imm ediately. The  motor was broken-in and  received th e full battery  of functio nal testing. A  vibration te st and the rmal function al test, identical to   the first  seque nce, were perform ed a nd th e  mech anism was pla ced into vacuum cyclin g. Tabl e 3 shows number of op eration s at st eps d uring the  second lifetime simulatio n seque nce.   Table 3.  HCM Life-T est Second Seq uence 

Oper ation Seque nce 2 Ops  Break-in CW Spin 56,200  Pre-Lifetest Fu nctional Testing 138,180  Vibration Test 138,180  Thermal F unctional Testing 704,340  Software Ve rification 727,570  Vacuum Ope ration 3,573,250  Post-Lifetest Fun ctional Testing 3,691,832  Additional Repea tability  Testing 4,276,882                    

Figure 13a & 13b.  Proto-Qualifica tion HCM Conta mination:  L ocking Fea ture on Mech anism  Scre w (left) and an Alum inum and Ch romate Par ticle Remov ed from the Bearing (righ t)  23