Multi-megawatt Space Power Reactors JOHN A. DEARIEN & JUDSON F. WHITBECK Summary In response to the need of the Strategic Defence Initiative (SDI) and long range space exploration and extra-terrestrial basing by the National Air and Space Administration (NASA), concepts for nuclear power systems in the multi-megawatt levels are being evaluated. The requirements for these power systems are being driven primarily by the need to minimize weight and maximize safety and reliability. This paper discusses the present requirements for space based advanced power systems, technological issues associated with the development of these advanced nuclear power systems, and some of the concepts proposed for generating large amounts of power in space. Design Requirements for Advanced Power Systems There are several areas at present, reflecting the needs of different groups, which are driving the design requirements of space based power systems. A brief summary of these groups and their requirements are discussed below. Strategic Defence Initiative Advanced weapon systems for the SDI require power in the multi-megawatt range with the unique requirement that the weapon, and therefore the power system, may be required to remain in orbit for years, unused, and then on a very short notice, be called on to operate for 100s of seconds at full power. This ‘burst’ mode of operation results in a much different set of design requirements than a normal baseload power station. Most of the weapon concepts for the SDI system utilize liquid hydrogen to cool the weapon and this hydrogen can be used, after cooling the weapon, as a coolant for the power system. In the case of nuclear power sources, the availability of this on-board hydrogen, in a sense ‘free’ after it has been used to cool the weapon, drives a power system designer quite naturally to the use of an open cycle Brayton system. A nuclear reactor heats the hydrogen, drives a turbine/generator with the resulting hot gas, and exhausts the gas overboard. Several of the concepts described in this section are of this type. Many of the weapon concepts of SDI have very sophisticated sensors and control systems on board and there is concern about the amount and composition of exhaust gases which can be tolerated in the vicinity of the weapon and not affect operation of John A. Dearien & Judson F. Whitbeck, Senior Program Specialists, Multi-megawatt Project, Technical Support Office, Idaho National Engineering Laboratory, Idaho Falls, Idaho, USA.
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