Radioisotope Electric Propulsion (REP): A Near-term Approach to Nuclear Propulsion
- Paper number
IAC-08.C4.7.-C3.5.3
- Author
Dr. George Schmidt, NASA Glenn Research Center, United States
- Year
2008
- Abstract
Nuclear Electric Propulsion (NEP) has been studied extensively for a variety of high-energy missions over the last several decades. NEP provides the performance benefits of electric propulsion, but unlike current systems based on solar power, NEP operation is not limited by distance from and orientation with respect to the sun. Almost all NEP studies to date have assumed the use of fission reactors as the nuclear energy source. However because of reactor criticality constraints, the system power per unit mass becomes very poor in the ~100 kilowatt power range for NEP spacecraft that could be launched with existing launch vehicles. This limits vehicle acceleration, increases mission time, and reduces spacecraft maneuverability in the vicinity of large gravity wells. This limitation is partially offset by the advantages of having abundant power available at destination for science instruments, communications and other payload operations. However, it is difficult to find science users with collective power requirements much more than just a few kilowatts. Although acceleration performance for reactor-based NEP generally improves with power, especially at multi-megawatt power levels, increasing power beyond several kilowatts has no real benefit for science. It also translates to larger radiators, more massive power processing equipment and generally larger spacecraft. There is a clear mismatch between science requirements, which favor smaller, faster spacecraft and several kilowatts of power, and reactor-based NEP, which favors large, 100-1000 kilowatt-scale spacecraft. It has recently been proposed that using Radioisotope Power Systems (RPS), instead of reactor power sources, could best fulfill the promise of NEP. Radioisotope Electric Propulsion (REP) has been evaluated before, but has not been seriously considered for flight due to the low specific-powers of traditional RPS (3-5 watts/kilogram). However, the prospects for REP have improved substantially with the advent of new higher specific-power RPS based on dynamic Stirling power conversion. NASA has initiated the development of an Advanced Stirling Radioisotope Generator (ASRG) with a specific-power target of ?8 watts/kilogram. When used with small ion or Hall thrusters, REP offers the specific impulse and acceleration performance of reactor-based NEP, but with much smaller, affordable spacecraft. REP would principally be used as an interplanetary stage for long-duration deceleration and acceleration in deep space. It would provide steady acceleration following launch to a positive Earth escape energy (C3) or boost by a chemical or solar-based electric propulsion stage. At remote destinations, REP would perform deceleration, orbit insertion and maneuvers around outer planets and other planetary bodies. REP-based spacecraft would also be able to provide plentiful power at destination for sophisticated science instruments and communications, and it would fit very nicely with the relatively modest kilowatt-scale power requirements of the space science community. This paper discusses how the ASRG and current ion and Hall thruster technology could open the door to many new REP-based missions. It compares the numerous REP studies performed over the last 10 years, and identifies the principal types of missions that would be enabled by the technology, specifically missions to the Trojan Asteroids, other small planetary bodies, and orbiter missions to the outer planets, moons, comets, asteroids, centaurs and Kuiper Belt Objects.
- Abstract document
- Manuscript document
IAC-08.C4.7.-C3.5.3.pdf (🔒 authorized access only).
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