Lessons Learned From the Development, Operation, and Review of Mechanical  Systems on the Space Shuttle, International Space Station, and Payloads  Alison Dinsel', Wayne Jermstad', and Brandan Robertson'  Abstract  The Mechanical Design and Analysis Branch at the Johnson Space Center (JSC) is responsible for the  technical oversight of over 30 mechanical systems flying on the Space Shuttle Orbiter and the  International Space Station (ISS). The branch also has the responsibility for reviewing all mechanical  systems on all Space Shuttle and International Space Station payloads, as part of the payload safety  review process, through the Mechanical Systems Working Group (MSWG). These responsibilities give the  branch unique insight into a large number of mechanical systems, and problems encountered during their  design, testing, and operation. This paper contains narrative descriptions of lessons learned from some of  the major problems worked on by the branch during the last two years. The problems are grouped into  common categories and lessons learned are stated.  Introduction  The Mechanical Design and Analysis Branch at JSC is responsible for the technical oversight of over 30  mechanical systems flying on the Space Shuttle Orbiter and the ISS. The branch houses the MSWG,  which has the responsibility to review all mechanical systems on all Space Shuttle Program (SSP) and ISS  payloads to verify compliance with the fault tolerance requirements as part of the payload safety review  process. These responsibilities give the branch unique insight into a large number of mechanical systems,  and problems encountered during their design, development, testing, and operation.  This paper describes some of the recent problems worked by the branch, and lessons that can be learned  from them to improve future mechanical systems. The paper contains narrative descriptions of some of  these problems. The problems are grouped into common categories and lessons learned are stated. The  categories used are derived from the Mechanical Systems Safety memorandum [l]. The letter has 11 key  design implementation and verification provisions to be followed to help ensure that credible failure modes  have been reliably and effectively controlled as a result of a thorough design, build, and test process for  mechanical systems. For this report, some categories will be combined, some omitted, and others  expanded upon, to arrive at the list of categories: binding, jamming, and seizing; fastener locking and  preload; strength; positive indication of status; and testing. Following each example, lessons learned are  stated.  Binding/Jamming/Seizing  This provision addresses the prevention of mechanism binding, jamming, and seizing. Appropriate design  features include dual rotating surfaces or other mechanical redundancies, robust strength margins such  that self-generated internal particles are precluded, shrouding and debris shielding, proper selection of  materials and lubrication design to prevent friction welding or galling, and others. Adequate dimensional  tolerances on all moving parts are needed to ensure that functional performance will be maintained under  all natural and induced environmental conditions. Tolerances associated with mechanical adjustment (or  rigging) must also be taken into account. Mechanical system designs must ensure compatibility of  lubricants used with interfacing materials, other lubricants used in the design, and the natural and induced  environments. Designs must also ensure that appropriate quantities of lubricant are specified.  * NASA Johnson Space Center, Houston, TX  Proceedings of the 3dh Aerospace Mechanisms Symposium, Langley Research Center, May 17- 19,2006  113