What if we could get to Mars in just 45 days?

Currently, sending humans to Mars would involve months-long missions launching at specific times. However, such long trips would not be risk-free for the astronauts on board and the best way to avoid them would be to shorten the travel time. To do this, nuclear energy seems ideal.

To leave Earth, we always rely on chemical rockets. The technology isn’t perfect, but it would still have allowed human exploration of the Moon. However, NASA, China and SpaceX have another target in mind: Mars. With chemical propulsion, we would then have to deal with a limiting factor: time. It would take approximately six to nine months (and a phenomenal amount of thrusters) to send men to the red planet.

Under these conditions, Mars would likely mark some sort of boundary beyond which we could not go. To travel further, you need to go faster with less fuel. What if the solution came from nuclear energy?

Nuclear Thermal and Electric

The idea is not new. NASA and the Soviet space program spent years working on the issue, but neither project really came to fruition.

There are two types of nuclear propulsion. Let’s start with the nuclear-thermal propulsion (NTP) involving a rocket engine in which a nuclear reactor replaces the combustion chamber. The latter burns liquid hydrogen as fuel to produce ionized hydrogen gas (plasma). This gas is then channeled through nozzles to generate thrust.

NASA became interested in the concept as early as the late 1950s with its program Nuclear Engine for Rocket Vehicle Application (NERVA). This resulted in the development of a successfully tested solid core nuclear reactor. With the end of the Apollo era in 1973, funding for the program was significantly reduced. The project was finally canceled even before flight tests were carried out. The Soviets also developed their own concept (RD-0410) between 1965 and 1980 before also canceling their program.

In turn, the nuclear electric propulsion (NEP) It is essentially based on a nuclear reactor supplying electricity to a Hall effect thruster (ion engine). The latter generates an electromagnetic field that ionizes and accelerates an inert gas (such as xenon). NEP designs are distinguished by being able to deliver over 10,000 seconds of specific impulse (I sp), meaning they can sustain momentum for nearly three hours. However, the level of thrust is still quite low compared to other options.

Both concepts have their pros and cons. That’s why researchers favor solutions that include two modes of propulsion (bimodal).

A few years ago, with Mars in sight, NASA relaunched its nuclear program with the aim of developing bimodal propulsion. According to the agency, such a rocket could allow transits to the Red Planet in just 100 days. However, a new concept proposes to do even better.

Artist’s conception of a bimodal nuclear rocket. Credits: NASA

March in 45 days

As part of the 2023 NASA Innovative Advanced Concepts (NIAC) program, NASA has selected a nuclear concept for Phase I development. This new class of bimodal nuclear propulsion system uses a “wave rotor cover cycle” and could cut the transit time to Mars to just 45 days.

The proposal is signed by Professor Ryan Gosse, from the University of Florida. It embodies one of fourteen concepts selected for phase 1 of this year’s NIAC (NASA Innovative Advanced Concepts) program, which aims to fuel visionary ideas. All teams will benefit from an envelope of US$12,500 to help mature the technology and methods involved.

Ryan Gosse’s proposal is a bimodal design based on a solid-core NERVA reactor (mentioned earlier). The latter would provide a specific impulse (I sp) of 900 seconds, which is double the current performance of chemical rockets. The proposed cycle also includes a pressure wave compressor – or Wave Rotor (WR). The technology, used in internal combustion engines, takes advantage of the pressure waves produced by reactions to compress the intake air.

Combined with a nuclear heat engine (NTP), the WR would use the pressure created by the reactor heating liquid hydrogen to further compress the reaction mass. According to the researcher, this could provide impulse levels comparable to that of a NERVA-class NTP concept, but with an intensity of 1400 to 2000 seconds of Specific Impulse. Combined with a CIP cycle, thrust levels would then be improved.

Ideally, the researcher promises that such a project could make it possible to get to Mars by only 45 days and potentially revolutionize human exploration of deep space. Such a transit would not only reduce the total duration of the mission, but also considerably reduce main risks associated with missions to Marsincluding radiation exposure and time spent in microgravity.

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