Adaptive fault tolerance for spacecraft

This paper describes the design and implementation of software infrastructure for real-time fault tolerance for applications on long duration deep space missions. The infrastructure has advanced capabilities for Adaptive Fault Tolerance (AFT), i.e., the ability to change the recovery strategy based on the failure history, available resources, and the operating environment. The AFT technology can accommodate adaptive or fixed recovery strategies. Adaptive fault tolerance allows the recovery strategy to be changed on the basis of the mission phase, failure history, and environment. For example, during a phase when power consumption must be minimized, there would be only one processor in operation. Thus, the recovery strategy would be to restart and retry. On the other hand, if the mission phase were in a time-critical mode (e.g., orbital insertion, encounter, etc.), then, multiple processors would be running, and the recovery strategy would be to switch from a leader copy to a follower copy of the control software. In a fixed recovery strategy, there is a specified redundant resource which is committed when certain failure conditions occur. The most obvious example of a fixed recovery strategy is to switch over to the standby processor in the event of any failure of the active processor.