Bolts a re tigh tened i n sequ ence to ensur e that they are en gagin g properly. Bolt pre-load is co ntrolled  with  Pre-Load Indi cating (PLI ) washers locat ed within the bolt mechan ism. The EVA  crewmembers will tighten  each bolt, in seri es, a p rescribe d num ber of rotation s before proceedin g to full torque. After all bolts are   fully tensioned, pre-l oad in  the capture bar is released by EVA reve rse actuation of t he capt ure latch and   the attachme nt process is compl ete. 

Each co rner fitting also inco rporates two continge ncy attachm ent bolt/nut combi nation s to allow a   structural co nnectio n to be made in the e vent the prim ary bolt can not be enga ged. A release mech anism,  an EVA-operated PIP pin, allows disconnection should the pri mary EVA bolt become l ocked i n the  sleeved nut after assem bly. RTAS desi gn also incl udes capabilit y to replace a nut (insert ) in the RTAS  fine alignme nt assembly. A threaded spacer serves to maintain  the gap bet ween the fine alignme nt  housing an d the co rner fitting so that no  bolt-ben ding loads a re created. Shea r is tran sferred  through th e  shear cylin der on the main bolt. 

RTAS Verification   The verifi cation of the RTAS was accompli shed i n a simil ar manner to the SSAS verification, using  toleran ce analysis, FEM analysi s, compone nt testing,  system l evel develop ment testing,  hard ware fit  checks an d finally mi ssion uniqu e dyn amic simul ation analysis. Since the captu re latch is common to  both  the SSAS and the RTAS, no additional component level verification beyond the capture latch verification  performed for the SSAS was requi red. The fine ali gnment bolt assembly testing closely parall eled the t wo  phase testin g perfo rmed  for the SSAS bolting sy stem. Acce ptance testin g wa s perfo rmed at th e  comp onent level and foll owed by a ssembly level verification  of com ponent locatio ns using the same  method s used for th e SS AS. The RT AS wa s successfu lly ope rated o n orbit to a ssemble  the P6 Truss  Element to the Z1 Tru ss Element. 

Common Attach Sy stem (CAS) 

The CAS i s another derivative of the SSAS used t o temporarily  attach vari ous payloads (experiment  pallets, l ogistics pall ets, et c) to the  S3 and P3  truss. The CAS in cludes the capture  latch mech anism,  three alignment guides and an umbilical mechani sm. The structural  attachment i s accom plished when the  captu re latch cla ws establishes a preloa d again st the alignme nt guides.   

CAS De sign Features a nd Operatio n  The CAS us es the same capture lat ch as SSAS; however , due to the alignment gui des being part of  the  load path, they are of a di fferent design (Figure 12). The berthi ng process is the same as SSAS except  once the latch is clo sed th e attachme nt is com plete (no bolting sy stem). Th e last operation i s to enga ge a  remotely operated um bilical  mechani sm (power and data). The umbilical m echani sm is driven  by either of  two inde pendent motor d rive mechani sms (sam e moto rs as used in the captu re latch) fo r redundancy and   has, additionally, a mechanical EVA-oper ated contingency override m echanism for the event of total   electrical failure.   

CAS Verific ation  The CAS uses  the same verific ation strategy as  SSAS with one exception. Each active CAS mus t be  compatible wi th all passive CAS. Unlik e SSAS, t he CAS des ign is not over-con strained and is  therefore  more compli ant to variations between assembli es. Similar to SSAS the CAS verification entailed hardware  fit checks and digital insp ection s. Du e to there bei ng only one p assive sim ulator, all possib le variation s  could not be verified. An analysi s of th e digital in spections i n conju nction  with the fit ch eck data is used to  verify the int erface will in deed acco mmodate worst-ca se tol erances. A vari ation of the CAS wa s used  successfully on orbit to sta bilize a nd te mporarily  attach the S0 Tru ss to the U.S.  Lab Modul e. 

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