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Extraterrestrial Fusion Reactors Could Unlock Limitless Energy—and Birth Human Space Civilizations, Physicist Claims

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Space-based fusion power could offer some advantages over its terrestrial counterparts, according to a new paper.
For instance, paper author Young K. Bae believes that space reactors could be “lightweight, modular, and scalable in ways that are severely constrained—or entirely infeasible—on Earth.”
Nuclear fusion has yet to become practical as a power source on Earth or in space, but Bae believes it could one day become a key part of space infrastructure.

For decades, scientists have tried to harness nuclear fusion—the process that powers stars—in reactors here on Earth. Currently, practical fusion is still a long way off, but there is enormous investment in this power source, because it could theoretically produce a virtually limitless supply of clean energy, perhaps exceeding global demand and enabling the transition to a decarbonized grid. Now, a researcher is pursuing a new twist on this longstanding goal: fusion reactors in space.

Picture massive doughnut-shaped reactors, known as tokamaks, floating in geostationary Earth orbit, or satellites blasting lasers across space to ignite fusion reactions. For now, these visions are speculative. But physicist Young K. Bae, PhD, believes that space-based fusion power could offer advantages over its terrestrial counterpart and may, one day, fuel the expansion of human civilization into space, according to his new paper published in the peer-reviewed journal Acta Astronautica.

“I’ve been working on this as an opening to a spacefaring civilization in the future,” Bae says in an interview. “That’s my goal right now—a footstep that humanity can build on.” While it’s not exactly a one-person job, Bae hopes to take a crack at it, he adds.

Bae is one of a small group of scientists interested in pioneering designs for fusion reactors in space. These structures could power off-Earth habitats, space manufacturing projects, orbital data centers, deep-space exploration, and all manner of other applications. His paper presents a rough roadmap toward a gigawatt-class tokamak—comparable to at least one large coal or nuclear plant capable of powering roughly one million homes—that might fulfill these lofty goals.

Space-based fusion power “enables higher power density for industrial-scale operations and deep-space missions where continuous power availability is critical” and “becomes increasingly advantageous at multi-gigawatt scales,” Bae writes in the paper.

Nuclear fusion occurs when two or more atoms merge into a single atom, a reaction that releases a colossal amount of energy. When you bask in the sun in the daytime or gaze at distant stars at night, you are experiencing the awesome power of fusion reactions. For more than a century, scientists have grappled with the tall technological order of reconstructing this process in reactors.

Tokamaks spark fusion reactions inside hot, charged plasma that is generated by powerful magnetic fields in donut-shaped torus chambers. This form of reaction, known as magnetic confinement fusion, has been demonstrated in tokamaks on Earth. While significant gains have been made, no reactor has ever come close to achieving “fusion breakeven,” which is a fusion reaction that produces more energy than was required to run the machinery that ignited it.

Bae’s paper suggests that space-based tokamaks might offer some advantages to ground-based versions. The microgravity environment could reduce the vast structural loads of tokamaks, and the lack of atmospheric pressure could significantly reduce the size and mass of vacuum chambers.

The study also speculates that the immense heat generated by a space tokamak could radiate directly into space with special panels operating at extremely high temperatures of roughly 1,340°F, which “could potentially dissipate heat more effectively on a mass basis than comparable terrestrial reactors,” Bae notes in an email.

And though the recent work focuses on magnetic confinement fusion in space, Bae is also optimistic that the other main type of fusion—known as inertial confinement fusion—could also be staged in space using high-powered lasers.

Bae has been pondering the potential of fusion power since he began his PhD at the University of California, Berkeley, in 1979. As part of his studies, he joined the fusion team at Lawrence Berkeley National Laboratory and became intrigued by this exotic power source. As his career progressed, Bae also developed a research interest in space exploration, which neatly dovetailed with his interest in fusion research. Like many space enthusiasts, he believes fusion power is the key to sustainable off-Earth settlements, such as orbital stations or cities on extraterrestrial worlds.

Earlier this year, Bae founded Spacefaring Research—a research institute based in Corona, California, that is dedicated to advancing space exploration—and serves as its chief scientist. Recently, he has floated the idea of space-based nuclear fusion to his former mentors and colleagues. Though the response from his peers was rather understated, he joked, his growing fascination with the topic inspired him to start crunching numbers.

“My colleagues know fusion, but they don’t know space engineering,” Bae says. “I happen to know both. So I said: ‘Okay, I’m going to combine these two knowledges and see what’s going on.’”

Currently, most spacecraft run on solar power, which is abundant near the sun but tapers off in more far-flung missions. To provide more reliable power, the United States and China are also vying to establish nuclear fission reactors on the moon, which would support astronauts in lunar bases by splitting atoms as opposed to fusing them. However, fission reactors raise safety concerns due to the risk of radioactive contamination, as well as security issues over the prospect of weapons-grade nuclear fuel in space (though there are currently no plans to use bomb-grade fuel in these reactors).

If space-based fusion power were ever realized—a big “if”—it could generate far more energy than solar or fission, potentially supercharging space exploration by providing off-Earth power plants that could fuel up spacecraft in orbit or support extraterrestrial bases on the moon or beyond. In addition, many previous studies have explored the possibility of fusion reactors as a form of ultra-futuristic spacecraft propulsion for huge passenger ships or even interstellar travel.

Of course, there would be significant costs to building a tokamak in space, as these facilities are, at minimum, dozens of feet in diameter. As a consequence, an orbital tokamak would need to be launched in modules to be assembled in space, similar to the International Space Station.

While research into space-based fusion reactors is sparse, other scientists are also making progress. Earlier this year in a preprint study, a team based in Singapore and China explored the concept of a massive space power plant that runs on uncontrolled fusion reactions. In his study, Bae also pointed to the pioneering work of Terry Kammash, PhD—a fusion expert at the University of Michigan who died in 2024—who had argued for the potential of space-based fusion power since the 1980s.

Bae hopes his research into the topic will inspire scientists to seriously consider the operational constraints and benefits of fusion reactors in space.

“I really want to have my daughter, or the next generation of my relatives—and humanity—to really step on it, so then they can go to space and live,” he says.

Cover of Popular Mechanics featuring "America's Nuclear Graveyard" with storage containers on a barren landscape.

Extraterrestrial Fusion Reactors Could Unlock Limitless Energy—and Birth Human Space Civilizations, Physicist Claims

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