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The requirements for performance by planetary exploration missions are increasing. Landing at a single location to take data is no longer sufficient. Due to the increasing cost, the missions that provide mobile platforms that can acquire data at displaced locations are becoming more attractive. Landers have also had limited range due to power limitations, limited lifetime of subsystems, and the inability to negotiate rough terrain. The Center for Space Nuclear Research has designed an instrumented platform that can acquire detailed data at hundreds of locations during its lifetime — a Mars Hopper. The Mars Hopper concept utilizes energy from radioisotopic decay in a manner different from any existing radioisotopic power source — as a thermal capacitor. By accumulating the heat from radioisotopic decay for long periods, though, the power of the source can be dramatically increased for short periods. Thus, a radioisotopic thermal rocket is possible. The platform will be able to ‘hop’ from one location to the next every 2—3 days with a separation of 10—20km per hop. Each platform will weigh around 50kg unfuelled which is the condition at deployment. Consequently, several platforms may be deployed on a single launch from Earth. With a lifetime estimated at 10 years, the entire surface of Mars can be mapped in detail by a couple dozen platforms. In addition, hoppers can collect samples and deliver them to the Mars Science Laboratory for more detailed analysis. Furthermore, the basic platform can be deployed to Europa, Titan, and even Venus with alterations — the propulsion system and operations essentially will be the same.

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An initial pre-concenptual CERMET Nuclear Thermal Propulsion reactor system is investigated within this paper. Reactor configurations are investigated where the fuel consists of 60 vol.% UO2 and 40 vol.% W where the UO2 consists of Gd2O3 concentrations of 5 and 10 mol.%.Gd2O3. The fuel configuration consisting of 5 mol.% UO2 was found to have a total mass of 2761 kg and a thrust to weight ratio of 4.10 and required a coolant channel surface area to fueled volume ratio of approximately 15.0 in order to keep the centerline temperature below 3000 K. The configuration consisting of 10 mol.% Gd2O3 required a surface area to volume ratio of approximately 12.2 to cool the reactor to a peak temperature of 3000 K and had a total mass of 3200 kg and a thrust to weight ratio of 3.54. It is not known yet what concentration of Gd2O3 is required to maintain fuel stability at 3000 K; however, both reactors offer the potential for operations at 25,000 lb f and and at a specific impulse which may range from 900 to 950 seconds. Nomenclature gGravitational acceleration, 9.81 m/s 2

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