When NASA announced a new Mars helicopter mission called Skyfall last week, the immediate response from most scientists had little to do with the ambitious plan to launch tiny, robotic aircraft to the Red Planet in December 2028. The bigger, more shocking news was that Skyfall would fly to Mars on a first-of-its-kind nuclear-propelled spacecraft.
“After decades of study and billions spent on concepts that have never left Earth, America will finally get underway on nuclear power in space,” said NASA administrator Jared Isaacman during a press event where Skyfall was announced.
The reveal stunned the U.S. planetary science community, whose official list of recommended future NASA missions hadn’t mentioned a nuclear-powered mission to Mars. Besides the “Who ordered that?” reaction, there’s also the matter of timing: in spaceflight terms, late 2028 is practically tomorrow, setting a too-close-for-comfort deadline even without the added complexity of NASA’s nuclear aspirations. How could the space agency possibly make this work?
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“A Possible Future”
No clarity has emerged from Scientific American’s repeated, unanswered phone calls and e-mails to NASA’s headquarters in Washington, D.C., and the agency’s Jet Propulsion Laboratory near Pasadena, Calif., where Skyfall’s predecessor helicopter, called Ingenuity, was born. Ingenuity, a tissue-box-sized robotic aircraft, made more than 70 flights on Mars between 2021 and 2024. Despite the space agency staying relatively mum about the finer details of its plan, a former senior NASA official, speaking anonymously, believes there’s reason for optimism.
“If somebody came into my office and pitched me a handful of Ingenuity helicopters to launch in 2028, and it’s [2026] right now, I would say, ‘Ah, it’s tight,’” the former official tells Scientific American. “But is it impossible? No. I’d like to see what the plans are…. The biggest indicator that this is serious will be to look at the budget, because a vision by itself is a dream—a vision and a budget is a possible future.”
Even within NASA’s multi-billion-dollar annual budget, there is no such thing as a free lunch. Most of NASA’s money is tied up in the space agency’s human spaceflight efforts: maintaining the International Space Station and pursuing the Artemis program to send astronauts back to the moon and build a permanent lunar base there. If Skyfall’s funding comes from human-spaceflight largesse, many scientists say, they won’t complain about new helicopters and a new nuclear-powered mission architecture. If instead funding comes from NASA’s far smaller planetary-science coffers, however, barring a significant budget boost, something else must die for Skyfall to fly.
Despite the risk that NASA’s nuclear ambitions could starve other parts of planetary science, Skyfall and the proposed nuclear-powered spacecraft should be seen as good news, says Paul Byrne, a planetary scientist at Washington University in St. Louis. “This is the kind of thing that NASA should’ve been doing in the late 1970s. Like, where the hell is our moon base? If this comes to pass—and there is an enormous ‘if’ here—it gets us to a NASA that many of us grew up hoping to see: people on the moon—with routine landings, nuclear propulsion that gets us to distant targets quickly, carrying large payloads.”
Plug-and-Play Propulsion
Skyfall is intended to reach Mars using a small, 20-kilowatt nuclear-powered spacecraft called Space Reactor-1 (SR-1) Freedom. Many elements of the spacecraft and reactor are either deep into development or already built, Isaacman said at the press event, with NASA taking the lead on the project and acting as the spacecraft’s “prime integrator” in partnership with the Department of Energy, which handles U.S. nuclear stockpiles.
Even so, the reactor itself has not been built, and it is distinct from a reactor that NASA intends to land on the lunar surface by 2030 and that is planned to power an outpost there. SR-1 Freedom’s main add-on will be repurposed from the Power & Propulsion Element (PPE) of NASA’s Gateway space station, a controversial Artemis initiative that the space agency effectively canceled last week. (This is familiar ground for the PPE concept. In a previous life, it was the core of NASA’s Obama-era Asteroid Redirect Mission, which had an estimated cost of $2.6-billion and was canceled in 2017.)
The legacy of nuclear propulsion is deep and star-crossed. In 1961, when President John F. Kennedy announced to the world that the U.S. would, before the decade was out, send humans to the moon and safely return them to Earth, he also committed funds to accelerate the development of a nuclear rocket. “This gives promise of some day providing a means for even more exciting and ambitious exploration of space, perhaps beyond the moon, perhaps to the very end of the solar system itself,” he said.
Four years later, in 1965, the U.S. launched SNAP-10A, which, to date, remains the nation’s only nuclear reactor to reach orbit. A predecessor, SNAP-9A, released about a kilogram of radioactive plutonium into the atmosphere after it failed to get to orbit in 1964. And several Soviet space reactors have also contaminated Earth with fissile material. Antinuclear public sentiment, budget cuts and regulatory challenges have scuttled subsequent U.S. space reactor programs ever since, fostering a widespread impression that bringing nuclear power back to the launchpad is more trouble than it’s worth.
Nevertheless, NASA has studied two types of reactor-based rocketry: nuclear thermal propulsion and nuclear electric propulsion. The former is the fastest feasible way to get astronauts to Mars, operating at a frightful peak temperature of 4,400 degrees Fahrenheit (2,425 degrees Celsius)—and venting radioactive exhaust—albeit only for short, intense bursts. Conversely, nuclear electric propulsion runs continuously but low and slow; it is capable of building great speeds over many years. Mated to the PPE, SR-1 Freedom will rely on the latter method; it will convert heat from its nuclear reactor into electricity to power xenon gas thrusters that produce no radioactive exhaust.
The reactor itself will be fueled by high-assay, low-enriched uranium—borrowing an approach from an ill-fated earlier project, the Demonstration Rocket for Agile Cislunar Operations (DRACO), which NASA had pursued in partnership with the Pentagon’s Defense Advanced Research Projects Agency. Conceived in 2023, the DRACO mission was a half-billion-dollar crash program to launch a nuclear thermal propulsion rocket by 2027 at the earliest. By using a larger amount of low-enriched uranium rather than a smaller amount of highly enriched weapons-grade stuff, DRACO was meant to sidestep regulatory red tape that could stifle the launch approval process. To simplify testing, DARPA designed it to switch on for the first time only after it was in space.
In 2024, however, the DOE added a requirement for ground testing, which would take years and hundreds of millions of dollars. DARPA abandoned the project in 2025.
“In many ways, DRACO was a half-technical, half-regulatory pilot program,” says Scott Pace, director of the Space Policy Institute at George Washington University. “I regretted its cancellation, as we lost an opportunity to pilot the regulatory approval process for putting a nuclear reactor in space.” Now, he says, the situation has possibly improved thanks to four executive orders, signed last year, that have streamlined some nuclear regulations.
“The policy foundations are absolutely there,” Pace says. “I’ve seen more positive support out of the Energy Department for doing things in space than I’ve seen since, probably,” the George H. W. Bush administration.
Better Late Than Never
Not everyone is so sanguine about NASA’s latest likelihood of nuclear success. Andrew Higgins, an aerospace engineer at McGill University, worries that the LEGO-like way that SR-1 Freedom has been planned—with lots of parts from different, unrelated projects just waiting to be bolted together—vastly understates the challenge ahead.
Although the nuclear spacecraft and the Mars helicopters are packaged together like peanut butter and jelly, there’s no obvious reason to combine the two, he says. “If you’re orbiting several moons of Jupiter or going to Neptune’s moon Triton, then nuclear electric propulsion makes sense. You have years and years for thrust to contribute,” Higgins says. But Mars, he adds, is too nearby for SR-1 Freedom to flex its muscles and build up high speed. Additionally, solar power is far more efficient for most destinations in the inner solar system. “Maybe SR-1 [Freedom] is fine as a demonstrator of running a nuclear reactor in space,” Higgins says, “but it won’t contribute to shortening a mission or bringing more payload.”
The realist view is that NASA wants to fly a nuclear reactor as soon as possible, and the Mars launch window justifies the aggressive development schedule (and commensurate funding) to appropriators. A December 2028 deadline also happens to coincide with the last month of the Trump administration’s term in office—timing that could help sustain White House support for the program and defend against any congressional cancellation attempts during its delicate, rushed development.
Why Skyfall, though? The answer is that this is the easiest possible Mars surface mission because the helicopters are basically print-to-order, and the mission won’t require a separate lander. In other words, sure, SR-1 Freedom makes no sense for Skyfall, but that’s okay, because Skyfall wouldn’t exist without SR-1 Freedom. Each, by necessity, hoists the other by its bootstraps out of abject improbability. And as a bonus, this reminds everyone that sending astronauts to Mars is the over-the-horizon goal for NASA’s moon-centric Artemis plan.
Whether the mission will launch in 2028 remains unclear—but thanks to Isaacman’s prominent support, its proponents say, Skyfall could make enough progress to ensure NASA sticks with it until 2030.
“Suppose it all worked, but it launched two years behind schedule,” the former NASA official says. “You think that would be a horrible failure? We would have nuclear electric propulsion! I would be cheering up and down.”