A nuclear rocket engine can halve the time spent traveling to deep space, which will also reduce the dose of cosmic radiation that the crew can receive and increase the amount of payload on board. However, the implementation of such a NASA engine is facing new challenges, writes Yelisey Khodolovsky.
In January 2023, NASA Administrator Bill Nelson said that the agency, in cooperation with DARPA, planned to develop and demonstrate nuclear rocket engine technology in 2027.
How a nuclear rocket engine works
Nuclear rocket engines, like conventional nuclear reactors at nuclear power plants, also work on the principle of uranium-235 fission, but the content of this isotope in their fuel must be higher. They also operate at much higher temperatures, making them extremely powerful and compact. Nuclear rocket engines have about 10 times the power density of a traditional light water reactor.
A nuclear engine may have an advantage over a chemical engine for several reasons.
It has a very high rate of exit of reaction products from the engine nozzle, creating high thrust that allows the rocket to accelerate faster.
These systems also have a high specific impulse. Specific impulse measures how efficiently fuel is used to create thrust. Nuclear engines have about twice the specific impulse of chemical engines, which means they can cut travel times in half.
Development of nuclear engines
The idea of a nuclear rocket engine is not new. Between 1955 and 1973, a number of nuclear rocket engines were manufactured and tested at the test site under the programs of NASA, General Electric and Argonne National Laboratories: Kiwi, NERVA, and others. One of them was even blown up to check how it would behave under a critical load.
But these projects used highly enriched uranium as fuel. This fuel is no longer used because of the current U.S. government’s fear of proliferation of nuclear weapons and nuclear materials.
Reducing enrichment
The so-called Global Threat Reduction Initiative, launched in 2009 by the U.S. Department of Energy and the National Nuclear Security Administration at the request of then-President Obama, was aimed at converting many research reactors that use highly enriched uranium to “high enriched low enriched uranium” or HALEU fuel.
In human terms, it would be more accurate to call it “intermediate enriched uranium,” with a U-235 content of 5% to 20%.
This “medium enriched uranium,” as you might guess, contains less fissile material than the highly enriched uranium fuel that was once used.
In an article for The Conversation, nuclear engineering expert Dan Kotlyar, an assistant professor of nuclear engineering at the Georgia Institute of Technology, noted that future expeditions will need more HALEU-loaded fuel on board (if they use it), which makes the engine heavier.
How to fly on a HALEU
To solve this problem, researchers are looking for ways to use such fuel more efficiently. However, a working solution is still a long way off.
The current course of the Biden administration, which involves increasing nuclear generation, has faced a serious shortage of enriched uranium, which is not enough for all consumers.
As previously reported, it is getting to the point where highly enriched uranium from research reactors and expired nuclear warheads is being fused with depleted uranium to produce the same HALEU for energy needs.
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