Environmental testing to prevent on-orbit TDRS failures

Can improved environmental testing prevent on-orbit component failures such as those experienced in the Tracking and Data Relay Satellite (TDRS) constellation? TDRS communications have been available to user spacecraft continuously for over 11 years, during which the five TDRS's placed in orbit have demonstrated their redundancies and robustness by surviving 26 component failures. Nevertheless, additional environmental testing prior to launch could prevent the occurrence of some types of failures, and could help to maintain communication services. Specific testing challenges involve traveling wave tube assemblies (TWTA's) whose lives may decrease with on-off cycling, and heaters that are subject to thermal cycles. The development of test conditions and procedures should account for known thermal variations. Testing may also have the potential to prevent failures in which components such as diplexers have had their lives dramatically shortened because of particle migration in a weightless environment. Reliability modeling could be used to select additional components that could benefit from special testing, but experience shows that this approach has serious limitations. Through knowledge of on-orbit experience, and with advances in testing, communication satellite programs might avoid the occurrence of some types of failures, and extend future spacecraft longevity beyond the current TDRS design life of ten years. However, determining which components to test, and how must testing to do, remain problematical.