Ohio State scientists advance focus on nuclear propulsion

COLUMBUS, Ohio – New developments in nuclear thermal propulsion technologies may soon enable advanced space missions to the farthest reaches of the solar system.  

Leading these advances are researchers at The Ohio State University: Engineers are developing a nuclear propulsion system that uses liquid uranium to directly heat rocket propellant as an alternative to solid fuel elements used by traditional nuclear propulsion systems.  

Their concept, called the centrifugal nuclear thermal rocket (CNTR), is specially designed to improve rocket performance while simultaneously minimizing any engine risk.  

While similar breakthroughs in the field have focused more on affordability than performance, CNTR potentially offers a substantial advantage for future crewed space missions even compared to other types of nuclear-powered systems in that it can approximately double an engine’s efficiency, said Dean Wang, a senior member of the project and an associate professor in mechanical and aerospace engineering at Ohio State. 

“In recent years, there has been quite an increased interest in nuclear thermal propulsion technology as we contemplate returning humans to the moon and working in cis-lunar space,” said Wang. “But beyond it, a new system is needed, as traditional chemical engines may not be feasible.” 

Chemical engines have been used in spaceflight since the very beginning of the space age.  However, they are limited in thrust, and use large quantities of propellant. Consequently, missions to the outer reaches of the solar system can take a very long time – nine years in the case of the New Horizons spacecraft that flew by Pluto.  

Because of these limitations, future missions will require propulsion systems that can reduce travel time, increase the amount of material sent on the mission, or both, if researchers want to safely send astronauts to far-off destinations — all vital reasons why demonstrating the potential of these approaches is so important, said Wang.  

“The longer you are in space, the more susceptible you are to all types of health risks,” he said. “So if we can make that any shorter, it’d be very beneficial.”  

If the team’s design is successful, implementing their engine in future rockets could make it easier to travel farther on less fuel, as the highest specific impulse — the amount of thrust achievable from a specific amount of propellant — of a chemical engine is about 450 seconds.  Nuclear propulsion engines based on designs tested in the 1960s achieved approximately 900 seconds and, according to the team, a CNTR could achieve even higher values. 

Utilizing nuclear thermal propulsion would also mean more flexibility for mission operations, as rockets could take advantage of additional flight trajectories not possible with chemical engines,  to help reach deep-space targets in shorter periods of time. More notably, because these systems can utilize a range of potential substances as propellant, widespread use could quickly facilitate the development of in-space resources such as asteroids and Kuiper Belt objects, said Wang.  

Overall, these heightened capabilities could allow quicker round-trip human missions to Mars as well as support novel one-way robotic missions to the outer planets, including Saturn, Uranus and Neptune, said Spencer Christian, a PhD student in engineering at Ohio State. Under John Horack, a professor of mechanical and aerospace engineering at Ohio State, Christian leads prototype construction of CNTR.  

“You could have a safe one-way trip to Mars in six months, for example, as opposed to doing the same mission in a year,” said Christian. “Depending on how well it works, the prototype CNTR engine is pushing us towards the future.” 

Despite these newfound avenues for increased space exploration, like with any emerging innovation, there are many engineering challenges that still have to be addressed, said Wang.  

“We have a very good understanding of the physics of our design, but there are still technical challenges that we need to overcome,” he said.  

Many of these challenges were detailed in a study the team recently published in the journal Acta Astronautica. Some potential hurdles include ensuring that the methods used for startup, operation and shutdown avoid instabilities as well as envisioning ways to minimize the loss of uranium fuel and accommodate potential engine failures. 

This team’s CNTR concept is expected to reach design readiness within the next five years — but in preparing their model for potential next-generation use, researchers are most looking forward to showing how well it could fare under extreme conditions.  

After all, a final laboratory demonstration will likely help inform the direction of future nuclear thermal propulsion technologies. “We need to keep space nuclear propulsion as a consistent priority in the future, so that technology can have time to mature,” said Wang. “It’s a huge benefit that we can’t afford to miss out on.”  

The team’s effort was supported by a grant provided by NASA.

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Contact: Dean Wang, Wang.12239@osu.edu

Written by: Tatyana Woodall, Woodall.52@osu.edu