1. Introduction
The primary considerations in determining whether or not redundancy is required have been whether or not the loss of a critical function would lead to the loss or severe degradation of a mission and whether or not redundancy could be implemented within the weight, power, and cost constraints of a mission. The decision to incorporate redundancy is made in part with the assumption that problems initiated by random faults can appear regardless of the amount of attention given to quality issues (such as how well an electronic box is made and the quality of parts that go into it).