Making a new case for space nuclear powerby Jeff Foust
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| “The understanding of the risks and the challenges of launching a reactor were probably underestimated in the beginning of that program,” DARPA’s McHenry concluded. |
Several months later, the agencies selected Lockheed Martin to develop the DRACO spacecraft (see “Nuclear space gets hot”, The Space Review, July 31, 2023). After that, though, DRACO faded into the background, with only occasional updates from the agencies. More recently, there had been reports that work on DRACO was slowing, or had stopped entirely.
It was not until the release of NASA’s fiscal year 2026 budget request at the end of May, though, that the public found out about DRACO’s demise. In a document filled with proposed cancellations of dozens of NASA missions, the agency said it was requesting no money for its share of DRACO. “The request also reflects the decision by our partner to cancel the Demonstration Rocket for Agile Cislunar Operations (DRACO) project,” the document stated, without further details.
A DARPA official later said that several factors contributed to DRACO’s demise. Rob McHenry, deputy director of DARPA, said at a recent webinar by the Mitchell Institute for Aerospace Studies that the agency started DRACO before what he called a “precipitous decrease in launch costs” by SpaceX as well as a reevaluation of whether NTP was the best approach.
“As the launch costs came down, the efficiency gained from nuclear thermal propulsion relative to the massive R&D costs necessary to achieve that technology started to look like less and less of a positive ROI,” he said. “So, the national security operational interest in the technology was decreasing proportionally to that perception.”
There was also growing interest in nuclear electric propulsion, or NEP, which offers much higher efficiencies in terms of specific impulse compared to NTP, albeit with lower thrust levels. NEP also offered the advantage of providing a source of electrical power—it uses a nuclear reactor to generate electricity for the electric propulsion system or for other applications—whereas NTP simply used the heat of a nuclear reactor to transfer energy to a propellant like liquid hydrogen.
“Nuclear electric is probably a more optimal long-term solution,” McHenry said. “That power in the space domain may be the critical enabler as much as the propulsion efficiency.”
He also suggested DARPA was running into problems testing DRACO’s NTP technology on the ground, citing “infrastructure barriers” for the project. “We want to do the disruptive tech. We don’t want to go spend massive amounts of money in improving core infrastructure of other government facilities.”
“The understanding of the risks and the challenges of launching a reactor were probably underestimated in the beginning of that program,” he concluded, leading DARPA to walk away from the project.
The announcement of DRACO’s demise was a first blow in a double-whammy for space nuclear advocates. The same NASA budget proposal that revealed DRACO’s cancellation also put no funding towards NASA’s own research into both NTP and NEP.
| The report noted the US had spent nearly $20 billion in constant-year dollars on space nuclear programs over the years, such as NERVA in the 1960s and Prometheus in the early 2000s, with little to show for it. |
“These efforts are costly investments, would take many years to develop, and have not been identified as the propulsion mode for deep space missions,” the document stated. “The nuclear propulsion projects are terminated to achieve cost savings and because there are other nearer-term propulsion alternatives for Mars transit.”
Congress may not go along with that move. A spending bill advanced by the Senate Appropriations Committee last week rejected the cuts, directing NASA to spend at least $110 million on nuclear propulsion. It also includes $10 million to create a “center of excellence” for nuclear propulsion research to be located in a region that does not have a NASA center but does have “a large population of industry partners who are also invested in nuclear propulsion research.” The House Appropriations Committee is scheduled to mark up its version of a spending bill that includes NASA later this week.
Powering up space nuclear
The cancellation of DRACO is the latest in a long line of setbacks for advocates of space nuclear power and propulsion. There have been few successes since the launch six decades ago of SNAP-10A, the first and only US space nuclear reactor.
“Everything since 1965, when we launched our first reactor, has fizzled despite billions invested,” said Bhavya Lal, former NASA associate administrator for technology, policy and strategy. “We remain in R&D purgatory, producing papers, not kilowatts.”
In the case of DRACO, she said, “nobody was asking for it, and when things got in a jam, it was easier to let it go.”
She was speaking at a Washington Space Business Roundtable event last week to discuss a new report she and Roger Myers, a former Aerojet Rocketdyne executive and member of the National Academy of Engineering, recently completed for the Idaho National Laboratory regarding development of space nuclear power. That report noted the US had spent nearly $20 billion in constant-year dollars on space nuclear programs over the years, such as NERVA in the 1960s and Prometheus in the early 2000s, with little to show for it.
“One core insight of our study is that the US didn't fail to deploy space nuclear systems because we lacked the physics or the funding or the people,” she said. “What we didn't have was mission pull, institutional coherence, and a sense of scale.”
Lal described a vicious cycle where a lack of demand, or “mission pull,” resulted in a lack of technology development and flight opportunities, and thus a lack of trust by mission planners in space nuclear technology. When there were nuclear programs funded, she argued agencies overreached, trying to do too much too quickly, like NASA did with Project Prometheus two decades ago. “Time and again we have tried to begin with building the space equivalent of the SR-71 when we should have started with the Wright Flyer.”
Those factors that have hindered development of space nuclear power are changing. One change, she noted, is the emergence of a mission pull for the technology. NASA, in its Moon to Mars Architecture development, recently identified fission power as its requirement for surface power on Mars missions.
Another is geopolitics. China and Russia have proposed developing megawatt-scale nuclear power systems for the International Lunar Research Station program they plan to establish in the south polar regions of the Moon.
“A continuously operating Chinese reactor on the lunar south pole would create de facto territorial control and justify exclusion zones under the guise of safety, and they would be right to do so,” she said, citing provisions of the Outer Space Treaty. That could require others to seek permission to land in the region to comply with that interpretation of the treaty’s language on avoiding interference. “In space as on Earth, first movers make the law.”
| “A 2028 ground test and a 2030 flight aligns with budget cycles, agency leadership terms, and congressional expectations,” Lal said. “Miss it and we risk stakeholders walking, funding drying up, and competitors defining the future without us.” |
In the paper, Myers and Lal call for the rapid development of a space nuclear power system, with or without propulsion. The goal is to have a system ready for ground tests in 2028 and an in-space demonstration in 2030. “We found that if we need to make progress in space nuclear, we need to begin with a small, manageable system on a timeline that keeps stakeholder interest,” Lal said.
The paper offered two approaches for doing so. One scenario, dubbed “Go Big or Go Home,” would develop a space nuclear power system capable of producing 100 to 500 kilowatts of power, which could be incorporated into a propulsion system. This would be a government-led effort with a potential cost of $3 billion.
The second scenario, “Chessmaster’s Gambit,” would fund parallel public-private partnerships for smaller systems of between 10 and 100 kilowatts. One track, involving NASA, would focus on a surface reactor that could be used on lunar missions and be later scaled up for Mars. A second track, for the Defense Department, would develop a reactor for in-space applications. Each would cost about $1 billion.
In either scenario, staying on schedule is key. “A 2028 ground test and a 2030 flight aligns with budget cycles, agency leadership terms, and congressional expectations,” she said. “Miss it and we risk stakeholders walking, funding drying up, and competitors defining the future without us.”
The report also included a third scenario, to be carried out in parallel with either of the other two, to develop new radioisotope power systems like the RTGs that NASA has long used for generating power for missions where solar was not an option. This effort would work to bring in new suppliers and use new isotopes, like americium-241 or strontium-90.
“Option three is low-hanging fruit,” Lal said. “It buys time, credibility, and momentum, no matter what, and it provides a fallback if larger efforts slip.”
The report didn’t express a recommendation for either of the two other scenarios, but she said it depends on the level of commitment and leadership. “Option one delivers transformational capability, no doubt, but demands extraordinary alignment and resources,” which she compared to the Manhattan Project. “Option two offers a more executable pathway, grounded in near-term missions and existing agency strengths.”
Either scenario is not an end in and of itself, Lal said, but a step towards greater capabilities down the road: “enduring presence on the Moon and Mars, propulsion to Mars, nuclear tugs in Earth orbit, power for peace and projection in contested regimes.”
“We’ve spent 60 years circling this problem. The pieces are finally in shape,” she concluded. “What we need now is resolve.”
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