| Abstract
The goal of this thesis work was to investigate a type of nuclear thermal rocket that has many of the advantages of open-cycle gas core rockets, while alleviating some of the drawbacks. Chemical rockets are limited in specific impulse due to the high molecular weight of the exhaust products, and the operating temperature. Solid-core nuclear thermal rockets can have much lower molecular weight exhaust (using hydrogen as propellant), but have operating temperatures no higher than 3000K due to the material limitations of the fuel. One possible solution is to use a gaseous fuel that can run at indefinitely high temperatures, but controlling the reactivity and containing the fuel has historically proven to be challenging. The current work focuses on a hybrid-fuel reactor with solid and gaseous fuel. The reactor cavity is surrounded by solid fuel which provides upwards of 50% of reactor power. This reduces the amount of gaseous fuel, which resulted in smaller reactivity fluctuations, and reduced fuel leakage while maintaining a high performance (with specific impulses still around 1600 to 2000 Sec.). Reactor designs were evaluated with MCNP6, and the specific impulse (and exhaust composition) was determined with NASA's CEA code. Hypothetical scenarios for conjunction-class Mars missions were compared to similar missions using chemical and conventional NTR propulsion. |