A Fusion Hybrid Propulsion System for Rapid Interplanetary Transport

Abstract

A fusion hybrid reactor whose fusion component is the gasdynamic mirror (GDM) is proposed as an energy source for a space propulsion system. The primary role of the fusion component is to supply neutrons to a blanket containing fertile material where they will breed ssile material and simultaneously burn it to produce power. Under these conditions, the fusion component need only function at or near \breakeven condition, a much less stringent condition than that required for a pure fusion reactor. A large aspect ratio GDM is desirable from the standpoint of MHD stability, and that allows for treatment of the system as semi-innite. With cylindrical symmetry, the performance of the system can be addressed by two, one-dimensional equations: one that describes the build-up of uranium233 in a thorium-232 blanket induced by the 14.1 MeV neutrons emanating from a DT burning fusion component, and another that describes the transport of these high energy neutrons in the blanket. We nd that for a reasonable design, such a hybrid reactor can produce hundreds of megawatts of thermal power per cm safely since it will operate as a subcritical system. When utilized for propulsion application, it is shown that it can generate a specic impulse of about 910 seconds at a thrust of about 0.455 mega-newtons. We assess such propulsive capability by addressing a round trip journey to Jupiter for the purpose of bringing to Earth 500 mT of He 3 which is known to exist abundantly in the atmosphere of that planet. Since approximately 1 mT of He 3 is required for a fusion reactor to produce about 2 GW-yrs of energy, one can readily see that 500 mT represents an ample supply of fuel that can meet a signicant portion of the world’s energy needs. Assuming that the He 3 on Jupiter has already been extracted and ready for shipment, the proposed propulsion system can make this cargo mission in about 4.7 years.