Design and performance analysis of a bimodal nuclear thermal rocket

Human and robotic spaceflight beyond the Earth and Moon will require the application of novel technologies to achieve the high thrust and propulsive efficiency‬ necessary for repeated orbital maneuvers. Proposed bimodal nuclear thermal electric propulsion (BNTEP) systems use a shared core to heat a propellant gas for nuclear thermal propulsion (NTP) and to generate electricity for nuclear electric propulsion (NEP). The combination of these technologies, in conjunction with electric thrusters, allows significant reduction in transit time for a notional mission to Mars. This project proposes a bimodal nuclear thermal rocket (BNTR) core, based on a variant of the tested Pewee nuclear thermal rocket fueled by high-assay low-enriched uranium, which modifies the moderator element design to include distinct channels for a helium-xenon (He-Xe) closed Brayton cycle power mode. To capture the coupled relationship between the neutronic and thermal-hydraulic (T/H) solutions in the core, a coupled framework is developed which interfaces Serpent Monte-Carlo neutronic solutions with coreThM, a reduced-order T/H solver. The T/H solution is verified using finite element analysis. The theoretical performance of the NTP and NEP systems in their respective propulsion and power operating modes is characterized. A burnup analysis is conducted to assess the performance of the core over the full duration of a notional mission with multiple burns and sustained midcourse operation. A final design configuration for a BNTR core is proposed which generates 50 kWe per engine with no adverse impact on NTP performance.