ing on the spacecraft, mission profile, power requirements and considerations of weight, safety, reliability and survivability. For deep-space missions, solar panels are not effective due to distance from the sun, batteries are impractical due to mission duration and fission-reactor systems are too heavy for this type of mission. Radioisotope generators provide a reliable source of power. Furthermore, radioisotopes provide localized component heating without the need for electrical wires, nor the efficiency losses associated with two conversion processes—thermal, to electrical, to themal. Thus, the technology of electrical power generation from radioisotope decay has been enabling for deep space missions such as those conducted in the 1970-1980s, those currently being readied for launch with Galileo and Ulysses, and those planned for the future. Safety Analysis Process A mission Final Safety Analysis Report (FSAR) is prepared for each US mission which uses nuclear power sources. An Interagency Nuclear Safety Review Panel (INSRP), composed of Department of Defense (DOD), Department of Energy (DOE) and NASA personnel, then generates a Safety Evaluation Report (SER) based on review of the FSAR and other available data. The mission agency (NASA) with inputs from DOD and DOE, weighs benefits verses risks, and makes a launch recommendation to the Office of Science and Technology Policy (OSTP). Launch approval must be granted by the OSTP, representing the President, or by the President himself. This paper will address the Final Safety Analysis Report prepared by the Department of Energy for the Galileo RTGs which has been completed and submitted to the INSIST for review [3]. A similar report has been written on the approximately 120 one-watt radioisotope heater units (RHUs) used on the Galileo spacecraft [4]. Figure 11 illustrates the process used to develop the safety analysis. Spacecraft and launch vehicle design and accident scenario data were provided by NASA [5], while DOE performed the source term determination and risk assessment portions of the analyses. The launch vehicle configuration, location and velocity can be used to characterize potential RTG accident environments during the various mission phases as indicated in Table I. The primary accident causes for each phase are generally the most active portions of the system during the phase. For example, during the propulsive phases, the most active portion is that system providing the propulsive thrust, the structure supporting the thrust and being acted on by external loads, and/or the guidance system. Multiple redundancies in the shuttle guidance system tend to decrease the likelihood of guidance failures for the shuttle.
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