High-energy-utilization, dual-mode system concept for Mars missions

A high-energy-utilization, dual-mode, electric pou er and propulsion system concept is described for a future crewed missions to Mars. The system uses a gas-cooled, nuclear reactor heat source and closed Brayton cycle (CBC) engines to convert thermal power to electricity. The He-Xe working fluid for the CBCs is also the nuclear reactor coolant. The fuel temperature and the inlet temperatures of the He-Xe of the nuclear reactor core and the CBC engines are kept almost constant during the propulsion and electric power modes to minimize thermal stresses. The temperature of the He-Xe exiting the nuclear reactor core is kept at least 200 K below the maximum fuel temperature. The electric power generated is kept the same during the propulsion and the power modes, but the reactor thermal power in the former could be several times higher. During the propulsion model the system's electric power, minus similar to1-5 kW(e) for housekeeping, operates a variable specific impulse magnetoplasma rocket (VASIMR). In addition, the reactor's thermal power, plus more than 85% of the heat load of the CBCs' radiators, is used to heat hydrogen. The hot hydrogen is mixed in the plasma exhaust of the VASIMR to provide both high thrust (>4000 N) and I-sp > 45,000 N . s/kg (similar to4,500 lbf.s/lbm), potentially reducing the travel time to Mars to 3 months. The system's electric power could also be used to support surface exploration of Mars. A dual-mode system based on the Pellet-bed reactor has a specific energy utilization of 400-500 W/kg and no single point failure. The system ran be tested fully assembled in a ground facility using electric heaters in place of the nuclear reactor. Operation and design parameters of a 40-kW(e) prototype are presented to illustrate the operation principle and demonstrated performance potential of the dual-mode system concept.