Renewed space exploration with multiple agencies planning crewed missions to Moon and Mars, requiring new technologies, such as Nuclear Thermal and Nuclear Electric Propulsion, reducing transit times to 45 days.
We live in an era of renewed space exploration, with multiple agencies planning to send astronauts to the Moon and beyond. To make this happen, new technologies are needed, particularly in the area of power and propulsion. Nuclear Thermal and Nuclear Electric Propulsion (NTP/NEP) is a top contender, and NASA has reignited its nuclear program to develop a bimodal nuclear propulsion system that could reduce transit times to Mars to just 45 days.
This proposal, titled “Bimodal NTP/NEP with a Wave Rotor Topping Cycle,” was put forward by Prof. Ryan Gosse and selected by the NASA Innovative Advanced Concepts (NIAC) program for Phase I development. This new class of propulsion system uses a “wave rotor topping cycle” and could reduce transit times to Mars to just 45 days.
Nuclear propulsion essentially comes down to two concepts, both of which rely on technologies that have been thoroughly tested and validated. Nuclear-Thermal Propulsion (NTP) uses a nuclear reactor to heat liquid hydrogen propellant, turning it into ionized hydrogen gas (plasma) that is then channeled through nozzles to generate thrust. Meanwhile, Nuclear-Electric Propulsion (NEP) relies on a nuclear reactor to provide electricity to a Hall-Effect thruster (ion engine), which generates an electromagnetic field that ionizes and accelerates an inert gas to create thrust.
Both systems have considerable advantages over conventional chemical propulsion, including a higher specific impulse (Isp) rating, fuel efficiency, and virtually unlimited energy density. While NEP concepts are distinguished for providing more than 10,000 seconds of Isp, NTP NERVA designs are the preferred method for crewed missions to Mars and beyond. This is why proposals that include both propulsion methods (bimodal) are favored, as they would combine the advantages of both.
Gosse’s proposal calls for a bimodal design based on a solid core NERVA reactor that would provide a specific impulse (Isp) of 900 seconds, and a pressure wave supercharger – or Wave Rotor (WR) – that would use pressure created by the reactor’s heating of the LH2 fuel to compress the reaction mass further. This would deliver thrust levels comparable to that of a NERVA-class NTP concept but with an Isp of 1400-2000 seconds. When paired with a NEP cycle, said Gosse, thrust levels are enhanced even further.
These and other nuclear applications could someday enable crewed missions to Mars and other locations in deep space, significantly reducing the major risks associated with missions to Mars, including radiation exposure, the time spent in microgravity, and related health concerns. With nuclear propulsion, a crewed mission to Mars could last only six and a half weeks instead of three years. This could revolutionize deep space exploration of our Solar System.