Seeded Hydrogen in Mars Transfer Vehicles Using Nuclear Thermal Propulsion Engines

What is it about?

A heavier vehicle can get to and back from Mars faster than a lighter vehicle provided that the additional mass is propellant. A vehicle propelled by a nuclear propulsion system has 3 main parameters that affect its performance: (1) the reactor power, (2) the propellant efficiency or specific impulse, and (3) the propellant density. Lower reactor power will require less propellant to be used to cool it down after a burn event due to reactor neutronics. This will allow more propellant in the propellant tank to be allocated to reducing travel time. Higher propellant efficiency or specific impulse will require less propellant to deliver the same thrust. This is assuming that sufficient thrust is delivered and that the vehicle does not spiral out of Earth’s gravity well. The propellant density tells the propellant mass that can be packed into a given volume. This is what increases the vehicle mass. Reducing the reactor power and increasing both the specific impulse and propellant density is the classical way of increasing vehicle performance and reducing travel time to Mars. However, you don’t get something for nothing. A reduction in reactor power by the addition of an impurity to the propellant with lower energy storage capacity than the base fluid can also increase the overall propellant density, however, specific impulse will suffer due to the higher molecular weight of the impurity. Increasing the specific impulse will push the average molecular weight of the propellant down which will likely result in a higher energy storage propellant with lower density. Therefore, there is a balance between higher specific impulse and the combination of decreased reactor power and increased propellant density. This paper examines the vehicle performance of hydrogen with argon as an added impurity.

Featured Image