The whole payload is the size of a silver dollar, and its entire job is to send one message after five days in the dark: I am still here.
That is Zeno Power's radioisotope heating unit, an americium-241 pellet producing five watts of thermal energy, riding a Firefly Blue Ghost lander to the Moon no earlier than 2028. When the lunar night falls and the surface drops to minus 170 degrees Celsius, the RHU will keep a small self-contained package—comms, power, thermal management—warm while every other payload on the lander freezes into what one report bluntly called "monument mode."
The requirement Zeno is building to is 120 hours. After that, per CEO Tyler Bernstein, the unit needs to "send a ping back and say, 'I am still here.'" That's it. That's the mission.
Now hold that image next to the language coming out of the White House. Executive Order 14369, signed in December 2025, set the goal of nuclear reactors in orbit "as early as 2028" and a lunar surface reactor "ready for launch by 2030." The OSTP memo implementing it, NSTM-3, directs parallel NASA and Pentagon design competitions for mid-power reactors delivering at least 20 kilowatts of electricity for three years in orbit.
The distance between a five-watt coin that has to prove it can survive one night and a 20,000-watt fission plant meant to run for years is the whole story. And the gap won't be closed by reactor engineering. It'll be decided by fuel, insurance, and whether Congress ever actually owns any of this.
Start with the federal architecture, because it's real and it's funded. NASA's SR-1 Freedom aims to fly a 20 kWe nuclear-electric propulsion system by the end of 2028, using the reactor to power thrusters and the repurposed Power and Propulsion Element from the canceled lunar Gateway. It's slated to drop three Ingenuity-class Mars helicopters—"SkyFall"—before heading deeper into the solar system.
Alongside it sits the LR-1 lunar reactor effort and NSTM-3's mandate for mid-power systems with both a fission-surface-power variant for the Moon and a propulsion variant for orbit. Money is flowing to NASA, the Department of Defense, and the Department of Energy through milestone-based competitions. Aaron Miles of OSTP called it, without irony, "a generational opportunity." Space nuclear, he said, "is indeed having a moment."
Then the practitioners started naming the constraints, and the moment got smaller.
The first is fuel. There is no production line for the ceramic high-assay low-enriched uranium—HALEU—that these reactors will likely need. DOE is the only domestic supplier, and it's already rationing. In July it allocated an unspecified amount to NASA for SR-1 and separately handed some to the reactor company Radiant.
The problem is that terrestrial nuclear wants the exact same fuel. Small modular reactors, the Army's Janus microreactor program powering bases—all of it draws from one thin supply. NASA's Jeremy Kenny put it carefully: "We have a good problem in that we need to be mindful of the availability of HALEU." Then the honest part: "That potentially could be a bottleneck in terms of prioritization and availability."
The Army's Jeff Waksman was more diplomatic about the competition: "Now is not the time for knife fights." But a knife fight over a scarce resource is exactly what shared fuel supply invites when everyone's timeline is 2028 to 2031.
The second constraint is insurance—and this is where the humble heater already teaches the flagship a lesson. Intuitive Machines is pursuing the same survive-the-night incentive, worth $15 million, on its own 2028 lander, also using an americium-241 RHU. Its nuclear space chief, Vince Bilardo, named the wall directly: NASA has to provide indemnification for the payload, because there is no commercial market to insure nuclear cargo.
"We can't fly that mission without that indemnification," he said. Read that again. A five-watt heater cannot launch without the federal government agreeing to backstop the liability, because no private insurer will touch it. Now scale that to a 20-kilowatt fission reactor.
The third constraint is people. Miles listed a workforce with both nuclear and space expertise as too small, plus limited access to ground test sites and a fragile supply chain for reactor components. The Army and NASA are already collaborating on Janus partly because the expertise pool is so shallow that parallel programs are really fighting over the same engineers.
And the fourth constraint is the one that undoes everything else: politics. Bhavya Lal, former NASA associate administrator and co-author of a 2025 study on the field's troubled history, put it as plainly as anyone has.
"What keeps me awake at night is, in three years' time, will we have a space nuclear program?"
Her diagnosis is the sentence the whole enterprise should be built around: support today is "positional, not structural. It is attached to people and not to paper. So, what happens in January 2029?"
Support today is positional, not structural. It is attached to people and not to paper. So, what happens in January 2029?
That date is a scalpel. SR-1 might launch on time in December 2028, just before the next administration takes office. But SR-1 has no clear customer. Its SkyFall helicopters could fly on something else. The lunar LR-1 doesn't depend on it. As Lal noted, "The only thing that truly needs SR-1 is SR-2, SR-3 and SR-4, and those don't exist."
We have been here. The United States has spent more than $20 billion across decades on space nuclear projects. Exactly one reactor has flown: SNAP-10A, in 1965, with every follow-on canceled. Lal's warning is that without Congress making multiyear appropriations—the one thing "a transition inherits instead of reviews"—the country repeats itself: "We may still fly one reactor, but it will be the same as 1965, maybe with better graphics."
Which brings us back to the silver dollar.
Bernstein called the Zeno demo not just a technology test but "a regulatory pathfinder." The launch-approval process for nuclear payloads was written years ago and exercised for the first time only recently, with City Labs' tritium-powered cubesat. Zeno's flight would be the first of a commercial radioisotope power source of this class. As Firefly's Farah Zuberi said, "The regulatory piece is going to be just as hard as the nuclear payload technology piece."
Here is the argument. The heater is cheaply flyable. It clears the boring obstacles first—launch approval, indemnification precedent, a real supply chain for americium-241, which Bernstein says the company is already building against future demand for "hundreds of these RHUs." And crucially, it does not need a customer that exists only on paper. NASA's survive-the-night incentive is a real check for a real capability that a lunar base plainly requires, because you cannot solar-power your way through a two-week night at minus 170.
The reactors, by contrast, are political promises attached to people. They need HALEU that isn't being produced at scale, indemnification that doesn't exist commercially, a workforce that's already stretched, and a downstream program—SR-2, SR-3—that hasn't been funded and could vanish the moment the current administration does.
None of this means the 20-kilowatt vision is wrong. It means the timelines are aspirational in the specific, unglamorous ways that have killed every prior attempt.
So watch the coin, not the reactor. If Zeno's five watts survive five nights and ping home, the field will have done something it has never reliably done: cleared the regulatory and supply-chain underbrush that actually determines whether nuclear hardware flies. That is a foundation a new administration inherits rather than reviews.
The reactors are betting they can outrun January 2029. The heater is betting it doesn't have to.