Nuclear Propulsion Explained

On paper, the Iₛₚ values for nuclear rockets are impressive compared to combustion-based propulsion. However, there is a significant drawback to nuclear propulsion. In chemical propulsion, an immense amount of energy is generated in seconds, and all propellant is consumed in minutes. Nuclear energy, on the other hand, typically generates energy over more than a year or in a fraction of a second, as in a nuclear weapon.

There is no standard device that can extract the full potential of a radioactive material in minutes to serve as the high-thrust engine of a launch vehicle. The only viable application is on a LEO-assembled spacecraft. A ship in LEO does not need to generate high thrust instantly; it can accelerate over time on an ever-expanding orbit until it reaches escape velocity.

The LEO-assembled space rocket I proposed utilizes ammonia fuel tanks cascaded in sequence (to allow the depleted tanks to be discarded to reduce weight), with the final module being the nuclear engine. The engine I proposed would generate 100 kW of thermal energy. Even this output is sufficient to inject the spaceship into a target planetary trajectory. Unlike a classical rocket’s burn duration of minutes, this architecture would require several hours to accomplish the same maneuver.

Compared to electrical ion thrusters, this nuclear thermal approach offers a critical advantage in thrust density. While ion thrusters provide high Iₛₚ, they produce minuscule thrust and require massive solar arrays that lose efficiency as the ship moves away from the Sun. Conversely, compared to chemical propulsion, the nuclear engine eliminates the combustion barrier. Chemical rockets are limited by the energy contained in molecular bonds, forcing them to carry massive amounts of propellant for very short burns. By using the Energy Multiplier, we achieve nearly double the Iₛₚ of the best chemical engines, allowing for a significantly higher payload-to-fuel ratio. This makes the 100 kW nuclear architecture the best choice—independent of solar proximity, more efficient than chemical stages, and more powerful than ion drives—perfectly suited for heavy payload delivery to the Moon or Mars.