An artist's conception shows a Mars transit habitat with a nuclear propulsion system. (NASA Illustration)
In what’s likely to be one of the last space policy initiatives of his administration, President Donald Trump today issued a directive that lays out a roadmap for nuclear power applications beyond Earth.
Space Policy Directive 6 calls on NASA and other federal agencies to advance the development of in-space nuclear propulsion systems as well as a nuclear fission power system on the moon.
“Space nuclear power and propulsion is a fundamentally enabling technology for American deep space missions to Mars and beyond,” Scott Pace, the executive secretary of the National Space Council, said in a White House news release. “The United States intends to remain the leader among spacefaring nations, applying nuclear power technology safely, securely and sustainably in space.”
Space-based nuclear power isn’t exactly a new idea: NASA and the Atomic Energy Commission considered thermal nuclear propulsion – a concept that would have involved heating up propellants with a nuclear reactor – way back in the 1970s as part of Project NERVA.
A different kind of nuclear power, which relies on using the heat from radioactive decay to generate electricity, has been used to power space hardware ranging from Apollo lunar surface experiments to the Curiosity rover on Mars. (NASA’s Perseverance rover, which is due to land on Mars in February, also has a radioisotope power system.)
NASA once considered putting a nuclear electric propulsion system on a spacecraft known as the Jupiter Icy Moons Orbiter, but that mission was canceled in 2005. Now there’s renewed interest in missions that require more power than can be generated by solar arrays – and that’s reviving interest in nuclear power for space applications.
An artist's concept shows a nuclear fission power system on the lunar surface. (NASA Illustration)
Nuclear energy has played a role in lunar exploration since the golden days of the Apollo moon program, when radioisotope power systems provided the wattage for scientific experiments.
Today such systems continue to power interplanetary spacecraft, ranging from the decades-old Voyager probes in interstellar space to the Perseverance rover that’s on its way to Mars. And now the U.S. Department of Energy and NASA are kicking things up a notch.
Tracey Bishop, deputy assistant secretary for nuclear infrastructure programs at the Department of Energy’s Nuclear Energy Office, provided a preview today during a virtual roundtable discussion focusing on the department’s role in space exploration.
She said potential partners from the nuclear power industry as well as the aerospace industry showed up for a “very engaging Industry Day” last month. “We’re looking forward to issuing a request for proposals from industry sometime this fall,” Bishop said.
The lunar demonstration project would follow up on the research conducted as part of the NASA-DOE Kilopower program, which successfully demonstrated a small-scale nuclear power system in Nevada a couple of years ago.
And that’s not all: The National Nuclear Security Administration, a semi-autonomous agency within DOE, is working with the Pentagon’s Defense Advanced Research Projects Agency on a road map for developing nuclear thermal propulsion systems.
It’s early in the process, but federal officials eventually plan to turn to industry experts for help in designing what basically would be a nuclear rocket engine, Greenaugh said.
The project — known as the Demonstration Rocket for Agile Cislunar Operations, or DRACO — would use nuclear power to heat rocket propellants to temperatures high enough to produce thrust. Such a system would be two to five times more efficient than conventional chemical propulsion, resulting in huge time savings for missions ranging from repositioning satellites to sending astronauts to Mars.
NASA and the Atomic Energy Commission tried to get a nuclear rocket called NERVA off the ground back in the 1960s.
“We did enough to understand what it was going to take, what the technical challenges are, and the fact that these [technologies] really are enabling for doing things such as certainly sending crews to Mars,” said Ralph McNutt, the chief scientist for space science at Johns Hopkins University’s Applied Physics Laboratory.
Project NERVA fizzled in the post-Apollo era, due to shrinking space budgets as well as growing safety concerns about nuclear power. But now America’s space ambitions are on the rise again, and next-generation nuclear power concepts are raising confidence that the safety concerns can be adequately addressed.
“The advanced modular reactors are certainly adaptable to be used in earthbound applications, too,” said former U.S. Rep. Robert Walker, who now heads a space policy consulting firm called moonWalker Associates. “That’s where a lot of the work is being done right now.”
Energy Secretary Dan Brouillette said following through on the concept could yield big payoffs.
“Nuclear propulsion could potentially cut the time of space travel to Mars by as much as half, which increases mission flexibility — which can be a true game changer for a Mars mission,” he said. “We’d like to get to Mars and back on ‘one tank of gas.’ That’s our goal, and that’s what we’re working for.”
Paul Dabbar, DOE’s under secretary for science, added that “it’s not just about getting to where we’re going, but it’s also about what we want to do when we get there.”
That’s where the interest in surface-based nuclear power comes to the fore. After all, if billionaires Jeff Bezos and Elon Musk envision building whole cities on the moon and on Mars, the power’s got to come from somewhere.
Eric Stallmer, president of the Commercial Spaceflight Federation, said future space settlements will almost certainly be built as public-private partnerships — with federal agencies like NASA and DOE blazing the technological trails for commercial ventures to follow.
“NASA has seen this in spades, when they did the development of resupplying cargo and crew to the ISS [International Space Station],” he said. “The government estimates that it saved between 20 and 30 billion dollars, compared to the traditional methods.”
So what will those extraterrestrial power systems look like? Will the moon go all-nuclear? Probably not, said Ben Reinke, executive director of the Department of Energy’s Office of Strategic Planning and Programs. Off-Earth settlements are more likely to rely on a mix of solar and nuclear power — plus batteries to store surplus electricity, as well as stores of hydrogen and oxygen that could be produced from ice on the moon or Mars.
“What you’re really talking about is a very small microgrid that has the same types of challenges that we have here on Earth,” he said. “You need some amount of power that would be baseload power. … And then on top of that, you would probably have some types of variable power, and a storage and distribution system that works for the proper size of that case.”
It turns out that nuclear fission isn’t the only option for energy on the moon: Reinke said lightweight, highly efficient perovskite solar cells could come into play. And who knows? Decades from now, nuclear fusion may even be part of the mix, with ample supplies of helium-3 fuel available on the lunar surface.
All of those technologies are part of the Department of Energy’s portfolio — so maybe Secretary Brouillette has a point when he says the DOE in his agency’s acronym could just as well stand for “Department of Exploration.”
Kilopower lead engineer Marc Gibson and Vantage Partner’s Jim Sanzi install hardware on the Kilopower assembly at the Nevada National Security Site during testing in March. (NNSS Photo)
That’s one small step for nuclear reactors on the moon and Mars, and several giant leaps to go.
Eventually, the technology pioneered by NASA’s Kilopower project could provide the electricity required to keep the lights on at off-Earth outposts, and to turn space resources into the breathable air, water and rocket fuel required for those outposts.
“When we go to the moon, and eventually on to Mars, we are likely going to need large power sources and not rely on the sun,” Jim Reuter, NASA’s acting associate administrator for space technology, explained today during a news briefing at Glenn Research Center in Cleveland.
The first step is to confirm that the technology works, reliably and safely. And officials from NASA and the Department of Energy’s National Nuclear Security Administration, or NNSA, say they did that during a series of tests conducted between last November and March at NNSA’s Nevada National Security Site.
