f the system level effects may require engineering functional analysis, simulation, fault injection, and statistical analysis to acquire a sufficient level of understanding. This activity is similar to the task of validation and verification of the adequacy of fault tolerance provisions which will be discussed in section 6.7. Spatial and Temporal Variation in the Charged Particle Environment [LaBel962] For most satellite orbit configurations the charged particle environment exhibits significant variance as a function of position within the orbit and at various times over the course of the mission. These dynamic characteristics of the environment are typically referred to as spatial and temporal variance respectively. In defining the requirements for system operations and for performing single event effects rate predictions, these variances must be reduced to a set of discrete conditions. Temporal variance connotes both the short-term and long-term variance in the severity of the charged particle environment. Long-term variance usually refers to issues such as the differences in particle populations between solar maximum and solar minimum conditions. Short-term variance captures the notion of average day particle population, versus the extreme populations present during peak solar particle event conditions. The average day conditions are often referred to as the normal environment in which a system must operate, and performance specifications such as availability or other measurable metrics of system performance must be assured under these conditions. Often the more severe of the long-term environments, solar maximum or solar minimum, are used to define this environment. The extreme condition present during solar particle event occurrence is usually defined as the worst-case environment and different system performance metrics may be established for these intervals. These system performance requirements are based upon mission requirements and the expected frequency of occurrence of the extreme condition. Spatial v