Figure of Merit for Fault-Tolerant Space Computers

To aid the computer designer in addressing the proper reliability goals, an economic model is proposed in which any increase in cost for reliability is evaluated against the expected decrease in cost of failure. These criteria are applied in an example to optimize the memory configuration of a computer that has a five-year lifetime requirement in space. An internal figure of merit is developed that can be used by the computer designer when little specific spacecraft and mission data are available. A more general external figure of merit can be used when mission parameters are defined. This latter is useful both for the computer designer and the spacecraft systems engineer.