The push for a new nuclear age to power the artificial intelligence boom with next-generation reactors remains feasible, but it is the U.S. military and NASA that are stepping in to accelerate the development of even smaller nuclear technology—so-called microreactors—to power remote bases, transform combat, and fuel deep-space exploration.

As the data center boom cools slightly and nuclear hype wanes—with stock valuations down and planned IPOs canceled—the federal government is increasing funding to support the deployment of microreactors on domestic military bases by 2028. Tentative plans call for eventually extending their reach to remote installations in harsh weather conditions, potentially near combat zones, and ultimately to lunar bases and the outer reaches of the solar system.

Antares first across the criticality line

In June, nuclear startup Antares successfully switched on its Mark-0 microreactor, first to the finish line in the Trump administration's pilot program race for next-generation reactors to achieve criticality.

Next, Antares aims to install its 1-megawatt R1 reactor at the U.S. Army's Fort Bragg in North Carolina by September 2028. Even more ambitiously, founder and CEO Jordan Bramble intends to place an R1-S—the "S" stands for "space"—on the moon as soon as 2030. In September, the Department of Defense awarded Antares $161 million to develop an R1-S reactor integrated with a spacecraft for flight certification. Solar power and radioisotopes are viewed as the shorter-term power solutions on the moon, with nuclear microreactors considered the permanent fix.

"We'll need fission power on the dark side of the moon," Bramble told Fortune. "Fission is going to be our best path to doing very high-powered things in orbit. If we're going to send landers to Europa and Enceladus and Triton (moons of Jupiter, Saturn, and Neptune) and try to find microbial life under the ice, we're probably going to need fission power to do that."

The concept is to deliver nimble, reliable baseload power that is clean, meltdown-proof, and relatively agile for limited power uses. The technology, however, still must be proven in the field commercially, not only in testing labs. Historically, the closest comparable applications have been within the Navy, which for decades has operated nuclear-powered submarines and aircraft carriers to avoid constant refueling.

"We've always believed since the beginning the [Department of Defense] would be the first adopter of advanced nuclear power," Bramble said. "That's obvious at this point."

Project Janus and the Army's bet

In the near term, the U.S. Army is working with Antares, Radiant, General Atomics, and others to install microreactors on its biggest Lower 48 bases to prove their reliability and protect critical defense infrastructure from grid failures. The effort, Project Janus, announced $2.2 billion in awards in August.

The largest recipient of the Janus awards is microreactor startup Radiant, which specializes in a transportable 1-megawatt reactor—enough to power about 750 homes—that takes up the space of "three parking spaces."

Radiant's ambitions for its 1-megawatt Kaleidos system extend far beyond the Lower 48 and its first projects at Fort Benning in Georgia and Buckley Space Force Base in Colorado, said chief operating officer and president Tori Shivanandan.

"The U.S. has struggled, and not just in major conflicts, in supporting troop deployments internationally," Shivanandan told Fortune. "If you're moving your troops around and you want defense systems to protect those troops as they're deployed overseas, you also need to make sure that you have the power available to defend your troops."

This year's war in Iran has demonstrated that U.S. military bases throughout the Middle East—and beyond—are vulnerable to drone attacks. Fuel convoys have historically been exposed as well, she said. Smaller, more mobile bases that require far less diesel refueling are a potential answer, she added.

"A diesel generator needs to be refueled every one to two days. In previous conflicts in the Middle East, those were our largest targets for our adversaries because fuel convoys create repeatable paths," Shivanandan said. "Our unit doesn't need to be refueled for three years."

The Army view

Jeff Waksman, the Army's top energy official, likes to recite the popular military saying: "Amateurs talk tactics, professionals talk logistics."

Waksman, a nuclear physicist by training, is leading Project Janus as well as the earlier Project Pele program for a transportable nuclear reactor. "As we look to the future of warfare, it is becoming increasingly electrical," he told Fortune, referencing drone warfare and more.

"We have a lot of applications where being able to have a lot of power, not needing to refuel for a long period of time, and being able to do that in a fairly transportable way could be absolutely game changing," he said, noting that Janus is the Roman god of new beginnings and transitions. "So, we are trying to lead the nation on these microreactors."

The Army's goal is to speed microreactors toward commercial success, making them more economical and more useful to the military. No company wants to buy the first few units while they remain economically prohibitive, so the Army is stepping in financially and then helping economies of scale take over. Project Janus plans to fund 20 microreactors for Lower 48 bases through the early 2030s.

Beyond that, "We are certainly thinking about what it would take to move reactors into more austere locations," Waksman said, citing tactically strategic positions in the Arctic or Pacific islands to power missile-defense systems and more. He is not ready to push for microreactors near combat, though. "We don't have any plans at this time to take these into conflict zones. We want to be clear about that.

"You can see into the future potential game-changing capabilities," he said. "But we need to see that this works safely and affordably within the Lower 48 states first." He cautioned against the Army—or the public—getting ahead of itself. "It's one thing to turn a reactor on for five minutes at low power. It's another thing to turn a reactor to full power, which nobody has done with these microreactors."

What is also clear is that the military sees nuclear the most reliable and steady power source for the future. The initial goal is not to power entire bases but to focus on the critical operations that must stay online during grid outages, especially in an age of AI and rising cybersecurity threats. The microreactors would serve as permanent power sources, not merely backup generation.

"Most of the electricity is not what we would necessarily consider critical, operationally critical. If people can't get lunch, that's a problem, but that's not national security critical," Waksman said. "We're focused on what the critical operations are on those installations."

Competing approaches

While many of the next-generation nuclear leaders are startups, the 71-year-old General Atomics also aims to trailblaze with an upgraded commercial version of its TRIGA training and research reactor, which was initially developed in the late 1950s.

General Atomics' GA-TES (Tactical Energy System) reactor, which would scale from 5 to 20 megawatts as needed, is first slated for Fort Hood in Texas.

Christina Back, General Atomics' vice president for nuclear technologies and materials, broadly agrees with Antares' Bramble that strong commercial demand for nuclear will sit at the two ends of the spectrum: large next-generation reactors, such as Westinghouse's 1.1-gigawatt AP1000, and microreactors. The mid-sized small modular reactors (SMRs) in development may struggle to find enough takers.

The GA-TES reactor is air-cooled, so it does not need to be positioned near water, unlike traditional light-water nuclear power plants.

"It's good for places that are remote. It costs a lot of money to move the fuel up there. You don't want to have to keep carting up coal or natural gas or whatever," Back said, citing locations from Guam to Alaska and noting that the General Atomics system only needs to be refueled every four to six years.

In competition with one another, the microreactor companies are not afraid to criticize each other, even if they avoid naming rivals directly. Back said General Atomics did not need to bother competing in the Trump administration's criticality race because the TRIGA test reactors have been proven for nearly 70 years.

Back also argued that a 1-megawatt reactor seems pointless, since the Army needs more power for a base and commercial demand is limited. Taking a microreactor into a combat zone is impractical, she added, because of the many days required to set it up and break it down.

General Atomics is well positioned and does not need to hype itself, she said. "As a company, we don't need to worry about the next Series A startup money, so we are very careful about what we say."

Radiant and others would of course disagree. Radiant's Kaleidos is focused on being the most transportable, while most microreactor systems are designed to stay in one place for prolonged periods of time—although they can be mobile. Shivanandan said she is most "confused" by the microreactor companies that require digging holes at least 50 feet into the ground.

"Once you dig a hole in the ground and put a reactor in there, that is a nuclear site forever," Shivanandan said. "You've limited the customer for those in-ground systems mostly to utilities. No [other] customer wants to be a nuclear cipher forever because business is changing incredibly quickly."

Where the rivals do agree is their enthusiasm for the Trump administration's efforts to expedite permitting for nuclear projects, as well as growing bipartisan support within Congress as the 2011 Fukushima nuclear disaster in Japan recedes from the forefront of people's minds.

"We tend to be very conservative because the nuclear industry can't afford an accident," Back said, before adding another dig: "We're [taking] a little bit longer than the 1-megawatt startups hurrying to show it works, because we're building something to last."

This story was originally featured on Fortune.com.