m level effects and consequences. In loosely coupled systems, a warm spare is periodically provided key checkpointing information to enable the processor to continue from the most recent checkpoint instead of having to begin tasks from initialization. This results in minimal impact due to recovery without incurring the overhead associated with the tightly coupled hot spare configuration. Fault Tolerant Systems Engineering [LaBe1962] [Banatre93] One of the more profound risks to spacecraft systems is that of having unknown device single event effects or failing to develop an understanding of the system level consequences of unmitigated single event effects. The criticality, or risk, of an operational impact to the system or spacecraft provides the foundation for setting the design requirement for single event effects management and mitigation. System level single event effects criticality analysis based on functional impact and the determination of appropriate mitigation techniques form the basis of a system engineering approach to the design of telecommunications satellite systems. The evaluation of alternative single event effects mitigation and fault tolerance provisions based upon the cost, power, size, weight, performance, reliability impact, and overall single event effects mitigation effectiveness of alternatives must be considered. The preceding sections have discussed some of the techniques available for fault avoidance, fault masking, and for detection and recovery operations. Each of these provisions has overhead associated with their incorporation into a system design, impacting size, weight, power, cost, reliability and performance of the system. Systems engineering must determine which techniques to utilize and how they must be integrated into the system in order to achieve cost effective systems which provide required availability and performance. At the onset of single event effects in the 1970s, the problem was constrained to the identification of the few components that exhibited susceptibility a