Artist's concept of a Fission Surface Power system on the Moon.
Credit: NASA
Before developing the final system, Houts and his team are testing with non-nuclear power for proof of concept.
"We're conducting tests in a thermal vacuum to learn about operating and controlling the system on the Moon," he says. "We're using resistance heaters to simulate nuclear heat. Electrical resistance produces heat."
After the test system proves the viability of the concept, the team could be directed to build the real thing, drawing heavily on U.S. and international terrestrial reactor experience.
"It would be built from stainless steel and fuelled by uranium dioxide. This combination has been used in terrestrial reactors throughout the world, so scientists and engineers are well versed in its operation."
The unit would not be active at launch, but would be turned on once in place on the lunar surface, where it would be surrounded by shielding to prevent any hazard from the radiation emitted.
"It would be very safe," says Houts. "And the beauty of the system is that it would be practically self-regulating."
Here's how it would work: Inside the reactor is a bundle of small tubes filled with uranium. Outside the reactor are control drums – one side of each drum reflects neutrons and the other side absorbs them, providing a way to control the rate that neutrons escaping the reactor core are reflected back in.
To start up the unit, the absorbent side of each control drum is turned out, away from the reactor core, so the reflective material faces in and sends escaping neutrons back in to the core. The resulting increase in available neutrons enables a self-sustaining chain reaction, which produces heat.
A coolant (sodium potassium mixture) flows through the passageways between the tubes, picks up the thermal heat produced by the reacting uranium, and transfers the heat to the Stirling engine. The Stirling engine then does its magic to generate electricity.
Meanwhile the coolant, which has 'downloaded' some of its cargo (heat) to the Stirling engine, circulates back through the reactor core, where it picks up heat and is ready to repeat the entire cycle.
The system would use only a minuscule amount of fuel – one kilogram of uranium every 15 years – and still have enough reactivity to run for decades.
"We give it a life expectancy of eight years, though, because something else would falter before the fuel would run out," says Houts.
After shutdown, radiation emitted by the system would decrease rapidly. A replacement system could easily be installed at the same site, and may be able to power not just outposts on the Moon, but Mars and future destinations as well.
Dauna Coulter is a writer for the U.S. space agency, NASA.
This is an edited version of a feature first published on the Science@NASA web site.
Solar on the moon? Please!
Solar on the moon? Please! On most of the moons surface there is roughly 2 weeks of light followed by 2 weeks of dark. Solar & batteries, at the moment, are just not up to the task!