replaced the setscrew with socket head cap scr ews which had a larger hex and could be driven  through the running torque.  • The pivot arm sub-assembly spring is retained on shaft with a 2.8 mm (0.112 in.) threaded end. A  self-locking nut is preloaded against the shoulder of t he shaft in the current design. In the original  design, the nut was not preloaded. The secondary locking feature to retain the nut was a cotter pin  through the threaded portion of the shaft. During the des ign, the shaft with the 1.5 mm hole (0.062 in.)  was viewed at enlarged scale. However, the CAD m odel did not include the minor diameter of the  thread. The hole left so little material that the lower end of the shaft snapped when the nut was  installed.  

EVA Interface Assembly  

EVA Interfac e Des cription   The EVA Interface is a standard 11.1 mm (7/16  in.) EVA-compatible double-height hex head. The  hex is locked from rotation with a disc that has a  12-point interface to the hex and a splined outer  diameter. The disc is spring loaded in the locked  position. The disc is disengaged by engaging a  deep well socket for the Pistol Grip Tool (PGT).  EVA  Hex  on  End  of   Shaft  EVA Interface Lessons Learned   It is critical to always  fully follow procedures  regardless of how familiar the operation has  become. The procedure calls for actuating the  interface using an extended deep well socket.  During initial functional testing, the same socket Lock  Disc       Figure 12.  EVA Interface Assembly    was always checked out from X-38 tool control. Howe ver, during static testing the vehicle was moved to  another location with a different set of tools. The stat ic test required functional testing before and after the  test. At some point during the testing, an ext ended socket was used. However, the socket was not deep  well and only partially disengaged the locking disc. When the interface was rotated, the hex ground into  the disc creating metallic chips. The interface a ssembly was disassembled and cleaned. A new disc was  installed. A placard referencing the procedure was in stalled to prevent the ev ent from occurring again. 

Fin/Rudder Sy stem Lev el Testing  Fin/Rudder Static Testing   The fins were statically tested while installed on the vehicle in both the depl oyed and stowed positions. In  the deployed position, the fins were tested to 100% of limit load. The S huttle program requires proto-flight  hardware be tested to 120% of limit load. However, the X-38 project decided to lower this requirement  because 1) the mid hinge/latch pair only had 0.05 margin  of safety, 2) the deployed fins only affected X38 mission success, not shuttle safety, and 3) 100% of limit load provided sufficient data for model  correlation. Reference “X-38 V-201 Integrated Structur al Test Plan – Aerosurfaces Tests” and “X-38 V201  Fin Deployed Test Report”. 

Conversely, in the stowed position ther e was greater uncertainty in the l oad, but also larger margin over  the design load. Therefore the fins were tested until the coupler links which are the lowest capability part  in the system neared the rated load fo r the turnbuckle. The fins were tested up to 218% of design load for  the stowed position. This provides additional test proven capability in the event that later analysis predicts  higher-than-expected fin loads during launch. Referenc e “X 38 V 201 Integrated Static Structural Test  Plan – Shuttle Launch & Landing Tests” and “X-38 V-201 Static Test Report – Shuttle Launch & Landing  Tests”.   Fin/Rudder Vibration Testing   375