Molten Salt Nuclear Rocket

The Nuclear Engine for Rocket Vehicle Application (NERVA) was a nuclear thermal rocket engine development program that ran for roughly two decades. Its principal objective was to "establish a technology base for nuclear rocket engine systems to be utilized in the design and development of propulsion systems for space mission application". It used hydrogen as the mono propellant. I would like to propose an alternative to this design.

The main objectives of my design are to improve the scalability of the design and reduce the environmental risks of a nuclear rocket. The scalability would be achieved by the use of liquid air as the mono propellant. Liquid nitrogen and oxygen have one of the highest expansion ratios. Cost of generating large amounts of liquid air and storing that is way cheaper than hydrogen. Additionally, due to high nitrogen content of the liquid air, it is much less corrosive compared to pure oxygen and hydrogen. This allows giant rockets to be built with high number of stages that can accelerate to very high speeds to reduce the time to reach the planets.

The environmental risks are reduced by a vertical trajectory, explained in my previous article. Additionally, the always on feature of a nuclear reactor compared to a combustion engine allows thrust to be generated upon entry to Earth’s atmosphere. While a rocket stage falls vertically on Earth, the aft skirts and interstages compress and push the ambient air into the engine. Then the air would be heated and pressurized by the nuclear reactor core and exhausted from the nozzle. This design requires the engine to be fed selectively by the mono propellant tank or the ambient air. The thrust generated by this approach would not be enough to land the stage safely on the ground. However, it would dramatically reduce the propellant reserve required for landing.

Finally, I propose molten salt reactors to be used as the reactor core. This allows more control on the nuclear reaction. Additionally, in a molten salt reactor the gaseous fission products (Xe and Kr) have little solubility in the fuel salt, and can be safely captured as they bubble out of the fuel. These byproducts can be pumped to the final stage of the rocket to be used as ion thruster propellant. Which are very expensive to obtain otherwise.