| Attention has recently turned toward the increased use of commercial off-the-shelf (COTS) computing equipment and software in space missions. Specific classes of missions, such as Space Shuttle payloads, limited lifetime low Earth orbit (LEO) satellites, and International Space Station experiments, can be flown without expensive space-rated computer hardware and custom software. This dissertation is aimed specifically at ultra-low-cost missions using COTS embedded systems in the space environment.; In order to raise COTS system reliabilities to sufficiently high levels, it may be necessary to implement appropriate fault tolerance techniques. Radiation-induced single event upsets (SEUs), while first identified as a source of spacecraft transient faults in 1975, are now being examined closely due to the greater susceptibility of commercial parts to the space radiation environment. Although many mechanisms to combat transient faults have been proposed and implemented in research laboratories, terrestrial computing systems, and previous space missions, not all methods are appropriate for ultra-low-cost space missions.; This dissertation analyzes factors related to improving the transient fault tolerance of spacecraft embedded systems, with particular emphasis on faults caused by SEUs. The following list summarizes the central issues which are discussed. (1) Concurrent hardware and software techniques for improving the transient fault tolerance of COTS embedded systems for ultra-low-cost spacecraft are explored. (2) Problems related to the way much of the research performed to date on COTS integrated circuits used in space missions are discussed, and an alternate way to approach such research is examined. (3) Field programmable gate arrays (FPGAs) are identified as an excellent technology for ultra-low-cost spacecraft, and the benefits provided by increased FPGA use in spacecraft embedded systems are studied. (4) An analysis of the impact of SEUs on embedded microprocessor caches is performed, and techniques are proposed to allow cache use in space missions. (5) Lessons learned while developing three ultra-low-cost spacecraft at the Colorado Space Grant College are discussed. Recommendations to future ultra-low-cost mission designers are made, and several avenues for future research are identified. |
