of travel as well as allow for shrinkage in the cabl e lengths due to decreases in temperature. The housing  that forms the floor and outside diameter  of the twist capsule is also us ed to clamp the outside race of the  main angular contact bearing pair. Once the cables are installed, the radial potentiometer locates on the  top of the outside walls of the caps ule and forms the lid of the system. The azimuth drive incorporates two  flex cables wound as a pair while the elevation driv e uses a single flex cable. In order to prevent  contamination from entering the system, a potting compound is used to seal the cable exit and entry  points at final assembly. Outside of the twist capsules , the flex cables are routed external to the gimbal  housings by a system of cable tracks and tie downs. Figure 6 shows the basic installation of the flex  cables into the gimbal azimuth drive.   

Figure 6.  Flex cable tw ist capsule installation 

Launch Lock System   The requirement for the first mode fundamental frequency of the gimbal during peak environmental  loading as well as the need to prevent the drives fr om back driving during these loads necessitated the  use of a locking system. The locki ng system on the HGAG uses a single pyrotechnic pin puller with  redundant NSI charges and an adjustable contact pad to restrain both the azimut h and elevation drives.  The pin puller and contact pad are cantilevered off the lower azimuth drive housing using a four-strut  mount. The pin in the pyrotechnic device engages an integrally machined flange in the elevation drive  twist capsule housing. The interface between the pyrotechnic pin and the housing flange is a spherical  bearing that is mounted into the end of the flange.  The spherical bearing helps to prevent over  constraining the assembly. The bearing also acco mmodates any angular misalignment that exists  between the four-strut mount and the housing flange that could result in increased pin pullout force or  binding. Because the housing flange is attached to the st atic portion of the elevat ion drive, this system  only effectively restrains the azimuth drive from rota ting. A second locking feature is required to lock the  elevation drive. The elevation driv e locking system uses both the elev ation drive internal hard stop and an  external adjustable contact pad to prevent drive rota tion in either direction. The contact pad is threaded  into a hole in the same four-strut mount that supports  the pyrotechnic pin puller.  Once the elevation drive  has been positioned for launch, the contact pad is adjus ted until it contacts a pin feature on the HGA  support arm (located on the rotating output stage of the elevation drive). After it is adjusted, it is locked in  place using a pair of locking nuts. 

The basic procedure for initially setting up the launch lock system is as follows: The azimuth drive is  driven to its launch position using motor encoder feedback.  At this point, the azimuth drive is not located  against any of its internal hard stops  because the pyrotechnic pin will re strain azimuth drive rotation in  both directions once it is installed.  The elevation drive is also driven to its launch position. For launch and  landing, the elevation drive is lo cated against one of its internal hard stops to prevent rotation in one  direction. After both drives hav e been positioned, the four-strut mount and pyrotechnic pin puller  assembly are positioned in the vertical plane such that the pin moves freely in and out of the spherical  245