In similar separation devices, an external system is utilized to ensure retraction of the preload bolt or rod.  However, in this application existing hardware was not compatible with the SSRD nor would it meet the  low shock requirements, therefore a new Retraction System was designed. The primary purpose of the  Retraction System is to carry the preload in the separation joint and retract the spherical rod end out of  the SSRD. The system is made up of a Preload Bolt, Retraction Spring, Spring Retainer, Shock Absorber,  and Bolt Catcher Can. The Retraction System is assembled in place after the BAA is mated to the  spacecraft. The Preload Bolt is threaded into the spherical rod end in the SSRD through the separation  fittings. The Spring Retainer and Retraction Spring are then fed over the Preload Bolt and the spring is  compressed. Once compressed, a washer and nut are threaded onto the Preload Bolt and the preload is  applied. Preload verification is done via a strain gage within the Preload Bolt to assure proper preload.  After applying the preload, the Bolt Catcher Can is installed to contain the assembly inside the spacecraft.  When the SSRD is actuated, the spring retracts the Preload Bolt and Spherical Rod End out of the SSRD  and across the separation plane, eliminating the possibility of hang up during separation. The Retraction  Spring also ensures positive retention of the Preload Bolt and Spherical Rod End throughout the lifetime  of the spacecraft. Figure 1 shows the components of the Retraction System.  Design Challenges  The majority of the design challenges were associated with using an SSRD as the primary restraint  device. As stated earlier, this device has never been used in a spacecraft separation system and had a  significant impact on the design of the Retraction System. There were two key design drivers on the  Retraction System related to the design of the SSRD: torque retention capability and mechanical  redundancy.  By design, the SSRD has no torque  retention capability within the unit except  for a key on the spherical rod end. Thic  posed a significant challenge on ho\n.  the unit is preloaded. The spherical rod  end within the unit needs to be held  fixed in its orientation such that the  friction critical surfaces between the rod  end and spool halves are not damaged  while preloading the unit. There were  two potential solutions to this challenge.  The first solution was to react the torque  through the key in the rod end. The key  is accessible through the SSRD housing  but reacting a torque load equivalent to  the 55.6-kN preload proved to be risky.  The second and chosen solution was a  unique hardware design used in conjunction with a torque tool to react the torque through the bus  structure and not the SSRD. The preload bolt has an external hex feature on the rod that interfaces with  an internal hex feature on the spring retainer. The fit between these two component parts allows relative  axial motion but both will rotate as an assembly. The spring retainer also has an external hex feature that  allows a tool to be installed and bolted to the aft bulkhead of the spacecraft. This tool constrains the  rotation of the spring retainer and preload bolt, but allows the bolt to stretch applying a preload. When  torque is applied to the preload nut bearing against the spring retainer, the torque is reacted through the  tool and onto the aft bulkhead of the spacecraft and not the SSRD. Figure 4. SSRD Torque Retention Tool  A key feature of the SSRD is it is a mechanically redundant device. It achieves this redundancy because  only one of the split spool halves needs to move laterally in order for the rod end to be released.  However, this is only true as long as the rod end is not constrained from exiting the unit. In order to  maintain mechanical redundancy at the system level, the retraction system needed to be designed such  152