9-1. Historical Overview of the US Use of Space Nuclear Power GARY L. BENNETT Summary Since 1961, the United States has successfully flown 35 space nuclear power sources on 20 space systems. These space systems have included the Apollo, Pioneer, Viking and Voyager spacecraft launched by the National Aeronautics and Space Administration and navigation and communications satellites launched by the Department of Defense. These power sources performed as planned and in many cases exceeded their power requirements and/or lifetimes. All of the power sources met their safety requirements. This paper surveys past uses of space nuclear power in the US and thus serves as a historical framework for other papers in this Conference dealing with future US applications of space nuclear power. Introduction The United States has used nuclear power on a number of technically sophisticated space systems which have greatly advanced our understanding of the solar system. In many cases, nuclear power was the only way to accomplish these missions. In the early 1950s, the US began studies of the use of nuclear power on spacecraft and by the late 1950s had active programs under way to develop both radioisotope and reactor power sources for spacecraft. The first actual use of a nuclear power source (NPS) on a spacecraft came in 1961 with the launch of the small SNAP-3B* radioisotope thermoelectric generator (RTG). In total, as shown in Table I, the US has launched 38 RTGs and one reactor to provide power for 23 space systems. (Thirty- five of these NPS on 20 space systems are still in space or on other planetary bodies.) The US has also used small radioisotope heater units (RHUs) on some of its RTG- powered science missions and on the Apollo 11 science package. All of the US RTGs have used 238Pu as the source of heat because of its long half-life (87.8 years) and its comparatively low level of radiation emission. The only US space reactor flown used 235U as the fuel [1,2]. Gary L. Bennett, National Aeronautics and Space Administration, Propulsion, Power and Energy Division, Washington, DC 20546, USA. Paper number IAF-ICOSP89-9-1. * SNAP is an acronym for Systems for Nuclear Auxiliary Power. All odd-numbered SNAP power sources used radioisotope fuel and all even-numbered SNAP power sources used nuclear fission reactors.
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