Explained: How nuclear-powered rockets can send missions to Mars in 45 days

Multiple agencies are planning to send astronauts to the Moon in the coming years as space exploration has been renewed in this era. Both NASA and China are also planning to send crewed missions to Mars within the next decade. Meanwhile, other countries are also likely to follow the suit in the upcoming years. However, missions that will take astronauts beyond Low Earth Orbit (LEO) and the Earth-Moon system need new technologies. These technologies range from life support and radiation shielding to power and propulsion. In the case of power and propulsion, Nuclear Thermal and Nuclear Electric Propulsion (NTP/NEP).
Bimodal nuclear propulsion: What is it
NASA relaunched its program to develop bimodal nuclear propulsion a few years ago. Bimodal nuclear propulsion is a two-part system that includes an NTP and NEP element. This system is expected to enable transits to Mars in 100 days. In 2023, the US space agency started a new program named NASA Innovative Advanced Concepts (NIAC) and has selected a nuclear concept for Phase I development.

This new bimodal nuclear propulsion system will use a “wave rotor topping cycle” that may reduce transit times to Mars to 45 days. This proposal was put forward by Prof. Ryan Gosse. Gosse leads the Hypersonics Program Area at the University of Florida and is also a member of the Florida Applied Research in Engineering (FLARE) team.
How will nuclear propulsion work
Nuclear propulsion is based on two concepts Nuclear-Thermal Propulsion (NTP) and Nuclear-Electric Propulsion (NEP).
The NTP system includes a nuclear reactor that will heat liquid hydrogen (LH2) propellant and turn it into ionised hydrogen gas (plasma) that will then be channelled through nozzles to generate thrust.

Meanwhile, NEP depends on a nuclear reactor to provide electricity to a Hall-Effect thruster (ion engine), which will generate an electromagnetic field that will ionise and accelerate an inert gas (for example xenon) to create thrust.
Both systems have major advantages over conventional chemical propulsion. These benefits include fuel efficiency, a higher specific impulse (Isp) rating and unlimited energy density (virtually).
Drawbacks of these nuclear propulsion systems
NEP’s advantage over NTP and conventional chemical propulsion systems is that it offers more than 10,000 seconds of Isp. This means NEP systems can maintain thrust for close to three hours. However, the thrust level is lower compared to conventional rockets and NTP systems. Gosse also explains an electric power source also raises the issue of heat rejection in space. In outer space, the thermal energy conversion rate is just 30-40% under ideal circumstances. The NTP NERVA designs are the preferred method for crewed missions to Mars and beyond. But, this method will face issues to provide adequate initial and final mass fractions for high delta-v missions.
Advantage of bimodal nuclear propulsion
The bimodal nuclear propulsion will be ideal as they will combine the advantages of both. Gosse’s bimodal design is based on a solid core NERVA reactor that will offer a specific impulse (Isp) of 900 seconds. This will be twice the current performance of chemical rockets. The bimodal system also includes a pressure wave supercharger or Wave Rotor (WR). This technology will be used in internal combustion engines that will harness the pressure waves that will be produced by reactions to compress air intake.

The WR would use pressure created by the reactor’s heating of the LH2 fuel to compress the reaction mass further when it is paired with an NTP engine. This is expected to deliver thrust levels comparable to that of a NERVA-class NTP concept but with an Isp of 1400-2000 seconds. Moreover, with this system thrust levels are also expected to improve.
A crewed mission to Mars based on conventional propulsion technology may last up to three years. However, A transit time of 45 days will reduce the overall mission time to months instead of years. This will drastically reduce the major risks associated with missions to Mars which include — radiation exposure, the time spent in microgravity and related health concerns.
Also Watch: