APPENDIX B IMPACT OF HOSTILE ENVIRONMENTS ON SPS Harry H. Holloway Manager, Projects Staff Vulnerability & Hardness Laboratory Defense and Space Systems Group of TRW Redondo Beach, California 90278 This discussion addresses the influence of natural radiation environment, and of some weapon environments, on the performance of the Satellite Power System. The discussion is generic, rather than system specific, in that it is concerned with classes of effects on equipment of the type that would probably be used to implement the Satellite Power System (SPS) design, rather than with an assessment of the system itself. The weapon environments considered include nuclear radiation from a weapons test, or an attack on another satellite, as well as direct attack by an Anti-Satellite Satellite (ASAT) carrying pellet, nuclear, or laser weapons. Effects are considered from the viewpoint of the pay load (solar array) as well as the vehicle-operating systems. Natural Radiation The natural radiation environments are the trapped-electron environment, the solar flare proton environment, and the trapped-proton environment, which all contribute to the total dose seen by the system. Current understanding of these environments probably is best exemplified by the NASA AE-7 model for electrons and the AP8MAC and AP8MIC models (also NASA) for protons. Exposure to the total dose environments, for both the payload (solar array) and the vehicle electronics, results in the gradual degradation of performance parameters. For the solar array itself, this degradation would result in a loss of power output of the order of 15 percent over 5 years in orbit. This kind of degradation is generally accounted for by including the end-of-life degradation in the initial design. For the SPS the degradation allowance would be sized to the refurbishment cycle time. Semiconductor devices in the vehicle electronics would be similarly affected, the degradation ranging from insignificant for most diodes and small signal transistors to potential catastrophic failure for some integrated circuit operational amplifiers. Hardening techniques available include mitigation of the dose incident on the parts by the use of added structural, box or piece part shielding, or by determination of the radiation sensitivity of the parts by test in a simulated radiation environment and providing for this radiation sensitivity in the design. This
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