Direct Fusion Drive For Advanced Space Missions

Executive Summary Princeton Satellite Systems and the Princeton Plasma Physics Laboratory (a Federally-Funded Research and Development Center) are collaborating on a breakthrough concept, the Direct Fusion Drive (DFD), a D – 3 He fueled fusion-powered rocket engine. The design is based on the Princeton Field-Reversed Configuration Reactor (PFRC) concept for a compact, clean, steady-state fusion reactor for power levels between 1 and 10 MW. Larger power levels can be accommodated using multiple engines. This technology enables missions such as human Mars orbiters, nuclear fusion powered space stations and high power robotic missions to the outer planets. This paper reviews the theory behind the design of compact and clean (aneutronic) fusion-powered rocket engines. The reactor employs a field-reversed magnetic field configuration (FRC) for plasma confinement, a novel radio-frequency (RF) method for plasma heating, and a unique method for control of propellant flow, producing a thrust of 30 N at a specific impulse of 2 × 10 4 s. The FRC has higher β (plasma pressure/magnetic energy density) than other magnetic plasma-confinement devices and a relatively simple linear solenoid magnet layout that permits control of propellant flow parameters. Higher β reduces the mass of the superconducting solenoidal coils needed for achieving the higher plasma temperatures required for aneutronic fusion reactions. Waste heat generated from the plasma's bremsstrahlung and synchrotron radiation can be recycled to power the RF heating and other on-board systems. The unique characteristics of this reactor –with non-equilibrium plasma conditions –will produce five-fold lower levels of neutrons than from equilibrium conditions. Additionally, the reactor design permits a novel method for extracting electric energy directly from the fusing plasma using the RF system. To produce fusion power with few neutrons, the reactor employs the D – 3 He reaction, which requires plasma temperatures about five times greater than the deuterium-tritium (D –T) reaction. A profound benefit results: the D – 3 He reaction can produce 20-times fewer and 5-times lower-energy neutrons than the D –T reaction per unit of power produced. Combined with the small size of the reactor, and its high surface-to-volume ratio, substantially less neutron-shielding mass is needed compared to mainstream D –T burning tokamak reactor designs; longer component lifetimes result. A sequence of two FRC test devices, followed by a prototype rocket engine, can be designed, built, and tested in four-year steps compared to the 30-year timeframe for design and construction of a single large D –T burning …