Manufa cturing   Failures assigned to thi s categ ory ha d root causes in the man ufacturin g process either f rom failure to   detect a mi s-manufa ctured  part or the i nability to manufac ture to the tolera nces called of on the drawi ngs.  Poor ide ntification of mand atory insp ection point s (MIP’s) on d rawings was dete rmine d to be a root ca use  on several P RACA’ s. Also , relian ce on very tight toleran cing to achieve sy stem  perfo rman ce lead to p arts  or asse mblie s that coul d not be manufa ctured to pr int and ultimatel y had to be accepted with waivers. 

The p rimary lesson le arned from thi s category should be the int egratio n of d esign and manufa cturing  engin eers i n the ea rly dev elopme nt of a me chanical syst em. In several cases the o riginal  design placed   unrealistic rel iance on ve ry tight manu facturin g control to assure systems performance. When these  requi rements were u nable to be met, rede signs and re analy sis we re requ ired to a ssure sy stems  perfo rman ce requi rements could be met . In several cases operatio nal limits h ad to be impo sed to assu re  that the ha rdware could perform.  Othe r cases i nvolved the failu re to dete ct mis-manufa ctured pa rts until  later te sting. The recurren ce control fo r all of the se probl ems wa s the additio n of ma ndato ry inspe ction  points to th e detailed design drawi ngs. The ad dition of MIPs to an y drawi ng should b e revie wed to assu re  that dimen sions that are critical  to syste m perfo rman ce are careful ly checke d during m anufa cture and n ot  left for a cceptance te sting t o catch.  Unle ss ide ntified as a MIP, m ost detail ed part dime nsions are n ot as  rigorously checked by qu ality inspecto rs. 

Fasten er   This category incl udes all cases where fasteners failed because eit her galling or the loss of a secondary   locking fe ature ca used a f ailure of a m echanism. Fo r exampl e, to meet payloa d safety requ ireme nts all  safety critica l fasteners must hav e a verified seco ndary locking featu re. This mean s that durin g  installatio n the runnin g torque of m ost interfe rence type lo cking ele ments have to b e verified. On  nume rous occasions the l oss of the se locking fe ature s resulted  in sig nificant rewo rk. Thi s does not  include time s when a stand ard repair was used to  replace th e locking eleme nt. In many cases modified o r  non-stan dard repai rs were neede d. Thi s cate gory also  includes failures whe re cycling of m ultiple use  fasteners resulted in galling. The root causes in these cases was attributed to a lack of or wear out of a  lubricated th reade d interfa ce. 

This category seems at first to be mo stly simpl e probl ems, h oweve r because it resulte d in al most 1 0% of  the po stproduction  problems on ISS it i s worthy of review fo r lesson s to redu ce the  risk of recurrence on  future develo pment projects. The use of secondary locking fe ature s is common in spa cecraft desi gn and  on m ost structural appli cations the re are few problem s because they are n ormally singl e use appli cation s  and failu res can be handle with sta ndard shop repairs. However, o n many ISS ap plicatio ns, fa steners a re  requi red to b e installe d and rem oved n umerou s times in the pre paratio n and use of the ha rdware. This  resulted in m any occu rrences of failed locking featu res that cau se signifi cant delays and costly repairs.  Many of the se problem s could h ave be en avoid ed if the ori ginal designs had accou nted fo r the n eed to  replace locki ng features as part of the normal processing of the ha rdware. S ome ISS designs utilized  easily repla ceable fa stener lo cking fe ature s and avoided this t ype of probl em. Another cau se of a  signifi cant n umber of failures was the  lack of p roper lubrication  of the fast ener or insert. Careful attention   should be made to  assure that galling  doe s not occu r at th e threade d inte rface between  fastener an d  insert or nut,  espe cially o n desi gns that may requi re seve ral in stallation/rem oval cycle s. In several   PRACA’s the root ca use was dete rmine d to be insufficient  lubrication, o r breakdown of exi sting lubrication  over seve ral fastene r cycl es. The co rrective action in many of  these cases was to eithe r add  a more  durable lub rication or ad d lubri cation to both the faste ner an d insert . 

Envir onment/Pr ocess   This catego ry was u sed to captu re failu res or hardware ano malie s caused by the system b eing ope rated   outsid e origi nal desi gn en vironme nts or operated in  a manne r not accounte d for in the ori ginal de sign.  Most of the se failure s or a nomalie s have happened on-orbit as a consequence of chan ges to the original  design p arameters an d assumptio ns. Although thi s is not n ormally co nsidered a d esign or hardware   probl em, this categ ory re presents an area wh ere nu mero us hardware proble ms had to b e worked an d  lesson s learned can be  drawn. These fail ures were a resul t of not a ssuring  that o riginal d esign  assumptions were actually th e environment or process that th e hardware was to be operated in. Often  it  was found th at early desig n assumptio n and operatio nal baseline s chang ed as the prog ram mature d. In  295