Fault Protection for the Space Interferometry Mission

The Space Interferometry Mission (SIM) is a deep space mission with limited ground contact and challenging instrument fault protection requirements. Some faults that could occur on SIM have symptoms only visible in the scientific measurements, and many of the observations that SIM makes must be repeated to be useful. Because of this, SIM needs to be very reliable. We are addressing these challenges by combining several approaches. The use of redundancy in the instrument will be important in making the complex instrument with several dozen actuators reliable. Probabilistic risk assessment and reliability modeling are being performed to study the most cost effective areas for redundancy. Ground checks are important parts of the fault detection approach. Special approaches such as "flood mode" (providing large amounts of raw data) and diagnostic data dumps are also important