It was President Donald Trump last week who issued a new directive to put NASA back on the moon using nuclear power.
Whereas chemical fuels are still considered best for launches, for example, and many satellites and other intraspace applications are fine for solar power, the Trump administration has said the idea of stationing humans on the moon requires a next-level energy system-and NASA agrees. For now, the agreement relies on well-established technology that is safely deployed around the world and is already in space.
“Space Policy Directive-6” is all about Space Nuclear Power and Propulsion (SNPP), an umbrella category that includes providing electrical and thermal power for planned installations on the Moon as well as the propulsion system that will likely eventually take NASA to Mars.
The White House explains on its fact sheet:
“Space nuclear systems power our spacecraft for missions where alternative power sources are inadequate, such as environments that are too dark for solar power or too far away to carry sufficient quantities of chemical fuels. Space nuclear systems include radioisotope power systems (RPSs) and nuclear reactors used for power, heating, and/or propulsion.”
Research radioisotope power systems (RPS) have been used safely for decades, and their design has helped inspire today’s emerging generation of nuclear microreactors, in fact. They are essentially closed systems in which an ongoing nuclear reaction generates energy, but with no moving parts.
In contrast to earth-based nuclear power plants, which in the current generation typically use nuclear energy to heat water into electricity-producing steam, these “nuclear batteries” use temperature difference alone to generate electricity.
Beyond explaining in detail what SNPPs are, what does this directive mean? Well, the fact that some technologies are in use today as terrestrial nuclear fission plants or satellite batteries doesn’t mean they can be put into lunar rovers or built on the lunar surface.
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Applications are different, environments are different, and even reliable technologies are constantly improving. This means that in 2024, when NASA plans to land the next man and the first woman on the moon, those astronauts will likely be using a whole new generation of nuclear batteries for their various tasks.
Indeed, NASA is already researching the best nuclear power plant for use on the Moon, adapting existing nuclear fission technology (which currently powers all nuclear power plants on Earth) to the special conditions on the Moon. This is a real challenge: the Moon has different surface materials, a different temperature range, much lower gravity, and so on.
Plus, whatever NASA designs, it has to be transported to the Moon in payload-friendly pieces. It’s like suddenly deciding to build a nuclear power plant on top of Mount Everest or on the bottom of the ocean: a completely different use case.
Moving forward, NASA is also interested in experimental nuclear reactors that are popular for research on Earth, such as fusion or molten salt. It doesn’t necessarily make sense to wait until fusion is mature before investigating how fusion might work on the surface of other planets or as a propulsion system for an intergalactic spacecraft. But for now, we have enough established technology to go to the moon.