A comparison of fusion/antiproton propulsion systems for interplanetary travel

Abstract

Rocket propulsion driven by either thermonuclear fusion or antiproton annihilation reactions is an attractive concept because of the large amount of energy released from a small amount of fuel. Charged particles produced in both reactions can be manipulated electromagnetically making high thrust/high specific impulse (7sp) operation possible. A comparison of the physics, engineering, and costs issues involved in using these advanced nuclear fuels is presented. Because of the unstable nature of the antiproton-proton (pp) reaction products, annihilation energy must be converted to propulsive energy quickly. Antimatter thermal rockets based on solid and liquid fission core engine designs offer the potential for high thrust (~10 Ibf)/ high 7sp (up to -2000 s) operation and 6 month round trip missions to Mars. The coupling of annihilation energy into a high-temperature gaseous or plasma working fluid appears more difficult, however, and requires the use of heavily shielded superconducting coils and space radiators for dissipating unused gamma ray power. By contrast, low-neutron-producing advanced fusion fuels (Cat-DD or DHe) produce mainly stable hydrogen and helium reaction products which thermalize quickly in the bulk plasma. The energetic plasma can be exhausted directly at high 7sp (. 10s) or mixed with additional hydrogen for thrust augmentation. Magnetic ftision rockets with specific powers (ocp) in the range of 2.5 to 10 kW/kg and 7sp in the range of 20,000-50,000 s could enable round trip missions to Jupiter in less than a year. Inertial fusion rockets with ocp > 100 kW/kg and 7sp > 10s could perform round trip missions to Pluto in less than 2 years. On the basis of preliminary fuel cost and mission analyses, fusion systems appear to outperform the antimatter engines for difficult interplanetary missions. *Senior Research Scientist, Advanced Nuclear Propulsion; currently, NASA Lewis Research Center, Cleveland, Ohio; Senior Member of AIAA. Copyright ©1987 by Aerojet TechSystcms Co. Published by the American Institute of Aeronautics Astronautics, Inc. with permission. 89 Purchased from American Institute of Aeronautics and Astronautics