We live in the era of space rescue, where several institutions are planning to send astronauts to the moon in the coming years. This will be followed by manned missions to Mars by NASA and China over the next decade, and other countries will soon join. These and other missions to take astronauts beyond low Earth orbit (LEO) and the Earth-Moon system require new technologies ranging from life support and radiation protection to power and propulsion.

As for the latter, nuclear thermal and nuclear electric motors (NTP/NEP) are the main ones! NASA and the Soviet space program spent decades researching nuclear propulsion during the space race. A few years ago, NASA revived its nuclear program with the aim of developing a bimodal nuclear engine, a two-component system of NTP and NEP elements capable of reaching Mars in 100 days.

As part of the 2023 NASA Innovative Advanced Concepts (NIAC) program, NASA has selected a nuclear concept for the first phase of development. This new class of dual-mode nuclear propulsion uses a “wave rotor spin cycle” and can reduce the transit time to Mars to just 45 days.

The proposal, titled “Closed Loop Wave Rotor Bimodal NTP/NEP”, was made by Professor Ryan Gosse, head of the University of Florida’s Hypersonic Program and a member of the Florida Applied Engineering Research (FLARE) team. Gosse’s proposal is one of 14 proposals selected by NAIC this year for the first phase of development, which includes a $12,500 grant to help develop the technology and methods. Other offerings included innovative sensors, instruments, manufacturing technologies, power systems and more.

A nuclear engine is basically reduced to two concepts, both based on technologies that have been extensively tested and proven. For a nuclear thermal engine (NTP), the cycle consists of a nuclear reactor that heats liquid hydrogen (LH2) and converts it to ionized hydrogen (plasma), which is then sent through nozzles to generate thrust.

Several attempts have been made to test this propulsion system, including Project Rover, a joint effort between the U.S. Air Force and the Atomic Energy Commission (AEC) launched in 1955.

In 1959 NASA took over from the US Air Force and the program entered a new phase dedicated to spaceflight applications. This eventually led to the Nuclear Propulsion for Rocket Vehicle Application (NERVA), a solid nuclear reactor that was successfully tested.

With the end of the Apollo era in 1973, funding for the program was drastically cut, leading to the program being canceled before any flight testing could take place. Meanwhile, the Soviets developed their own NTP concept (RD-0410) between 1965 and 1980 and conducted a single ground test before canceling the program.

A Nuclear Electric Propulsion (NEP), on the other hand, relies on a nuclear reactor to provide electricity to a Hall effect motor (ion thruster), which creates an electromagnetic field that ionizes and accelerates an inert gas (like xenon). . Attempts to develop this technology include NASA’s Nuclear Systems Initiative (NSI) Project Prometheus (2003-2005).

Both systems have significant advantages over a conventional chemical engine, such as higher specific thrust (Isp), fuel efficiency and virtually unlimited energy density. While NEP concepts are unique in that they provide more than 10,000 Isp, meaning they can maintain thrust for about three hours, the level of thrust is considerably lower compared to conventional rockets and NTPs.

The need for an electrical source also raises the issue of heat removal in space, where the conversion of thermal energy is 30-40 percent under ideal conditions, Gosse says. And while NERVA’s NTP designs are the method of choice for crewed missions to Mars and beyond, this method also has problems providing appropriate initial and final mass fractions for high delta-v missions.

Therefore, proposals that include both methods of movement (bimodal) are preferred, as they combine the advantages of both. Gosse’s proposal includes a bi-mode design based on a solid-core NERVA reactor that would provide a specific impulse (Isp) of 900 seconds, twice the current performance of chemical rockets.

The cycle Gosse proposes also includes a pressure wave supercharger or wave rotor (WR), a technology used in internal combustion engines that uses pressure waves created by reactions to compress intake air.

Paired with the NTP engine, the WR will use the pressure created by heating the LH2 fuel in the reactor to further compress the reaction mass. As Gosse promises, this is comparable to the NERVA-class NTP concept, but will provide thrust levels with an Isp of 1400-2000 seconds. Combined with the NEP cycle, Gosse said, craving levels are even higher:

“Combined with the NEP cycle, the Isp duty cycle can be further increased (1800-4000 seconds) with minimal dry matter addition. This bi-modal design provides rapid transit for manned missions (45 days to Mars) and revolutionizes deep space exploration of our solar system.” .

With conventional engines, a crewed Mars mission can take up to three years. These missions will begin every 26 months when Earth and Mars come into closest approach (aka Mars opposition) and spend at least six to nine months on the way.

A 45-day pass will reduce the overall tenure to months rather than years. This would greatly reduce the main risks associated with Mars missions, including radiation exposure, time spent in microgravity, and associated health issues.

In addition to engines, there are proposals for new reactor designs that will provide a stable power supply for long-term ground missions where solar and wind power are not always available. Examples include NASA’s Kilopower Reactor Using Sterling Technology (KRUSTY) and the hybrid fission/fusion reactor selected for the first phase of development by NASA’s selection of NAIC 2023.

These and other nuclear programs will one day enable manned missions to Mars and other places in deep space, perhaps sooner than we think! Source