Optimal Designs of Mobile Nuclear Engines to Power Manned Vehicles On Mars

This work develops original conceptual designs for compact nuclear fission reactor engines to power robust mobile equipment operating on the surface of the planet Mars. This is a nuclear application area not well explored in previous publications. Some novel analytical approaches are developed herein, including the application of optimal control theory to minimize radiation shielding mass. This work also provides the first study of using another planet's atmosphere to implement open-cycle thermal conversion systems.

To power equipment on Mars for extended durations at sustained power levels ranging from one hundred horsepower to several thousand horsepower, there is no practical alternative to a nuclear fission heat source. Design difficulties arise from mobility's need to restrict engine size and mass, each of which is, in turn, determined by the schemes chosen for thermal conversion waste heat rejection and for neutron and gamma radiation shielding.

The conceptual design solutions pursued herein entirely avoid a large waste heat rejection radiator or low pressure heat exchanger by instead using the martian air directly as the thermal conversion fluid. This Open Brayton Cycle implementation unconventionally employs large-diameter radial-flow compressor/turbine designs for the lower pressure air-flow stages in order to obtain sufficient efficiency from the low pressure martian air. Design prescriptions and analyses for these rotating components are included.

The radiation shielding mass has been minimized by numerical algorithms developed as part of this work to solve the Euler-Lagrange equations for a minimum mass shield meeting stated radiation leakage requirements. In addition, a risk-balancing approach is taken to setting those radiation requirements in order to avoid excessive conservatism.