Nuke the Moon: Project A119

Podcast Transcript

At the height of the Cold War, the United States considered a plan so audacious that it sounds like science fiction: detonating a nuclear weapon on the Moon.

Known as Project A119, the idea was born from fear, prestige, and the urgent need to answer the Soviet Union’s early lead in space.

The plan was real, the scientists involved were some of the most noteworthy of the 20th century, and the implications were enormous.

Learn more about Project A119 and the quest to nuke the Moon on this episode of Everything Everywhere Daily.

To understand Project A119 and what would drive people to want to nuke the moon, you must first appreciate the atmosphere of near-panic that gripped the United States in the autumn of 1957.

During the Cold War, the Soviet Union took the lead in the Space Race with the launch of Sputnik 1 on October 4, 1957. That small, beeping aluminum sphere, roughly the size of a beach ball, shattered American assumptions of technological supremacy and raised a terrifying strategic implication: if the Soviets could put a satellite into orbit, they might be able to deliver a nuclear warhead anywhere on the planet.

It was in this environment of anxiety and fear that someone in the United States Air Force asked a question that would have seemed insane in any other era: What if we detonated a nuclear weapon on the Moon?

This idea didn’t come out of nowhere. According to press reports in late 1957, an anonymous source had disclosed to a United States Secret Service agent that the Soviets planned to commemorate the anniversary of the October Revolution by detonating a nuclear device on the Moon to coincide with a lunar eclipse on November 7.

Whether this rumor was genuine intelligence or Soviet disinformation was unclear at the time, but it reinforced the idea that the Moon was about to become a theater in the Cold War.

The intellectual groundwork for thinking about nuclear explosions in space had already been laid. Edward Teller, the “father of the H-bomb,” in February 1957, proposed detonating nuclear devices both on and at some distance from the lunar surface to analyze the effects of the explosions.

The Armour Research Foundation (ARF), based at the Illinois Institute of Technology in Chicago, had been positioned for exactly this kind of study for years. ARF began studying the effects of nuclear explosions on the environment in 1949, and by 1958, it had become the natural home for such studies.

Project A119 was a top-secret plan developed in 1958 by the United States Air Force. The name was deliberately dull. It was the kind of bureaucratic title designed to be forgotten in a filing cabinet. However, the contents of the plan were anything but ordinary.

In 1958, Dr. Leonard Reiffel, who worked at the Armour Research Foundation, was asked by the Air Force to “fast-track” research into what a nuclear explosion would be like on the Moon.

Reiffel was born in Chicago in 1927 and collaborated with Enrico Fermi, who created the first atomic reactor at the University of Chicago. He was rigorous, discreet, and politically savvy enough to understand what he was really being asked to do.

The plan was laid out in a paper titled “A Study of Lunar Research Flights – Volume I,” which described the following scenario: the United States Air Force would launch a rocket to the Moon carrying an atomic fission bomb, as a hydrogen bomb would be too heavy for the mission, and once it reached the Moon, avoiding any crater, it would explode.

There were two layers to this project. The surface layer was scientific: the explosion might reveal something useful about the Moon’s geology and composition through patterns in ejecta and seismic activity. But the deeper purpose was purely psychological and political. The Air Force wanted to surprise the Soviets and the world by saying, “Hey, look at what we can do. We can blow up the moon”.

A visible detonation on the lunar surface, seen by millions of people around the world without the aid of any telescope, would declare American technological capability in the most dramatic terms imaginable.

The target was chosen carefully. Detonation was to occur strategically along the Terminator Line, the border between the Moon’s light and dark sides. This was not an accidental choice. A blast along the terminator would be illuminated by the Sun at a low angle, maximizing the visibility of any expanding dust cloud against the darkness of the lunar night.

A ten-member team, led by Leonard Reiffel, was assembled at the Illinois Institute of Technology in Chicago to study the potential visibility of the explosion, the benefits to science, and the implications for the lunar surface.

One of the members was Gerard Kuiper, who was one of the most distinguished planetary scientists of the twentieth century. He was the man whose name would eventually be given to the disk of icy bodies beyond Neptune, the Kuiper Belt. His presence on the team gave it scientific credibility. But his most consequential contribution may have been his recommendation to bring in a particular graduate student, Carl Sagan.

Carl Sagan was then a graduate student who modeled how the gas-and-dust cloud would expand in low gravity. Sagan was just 24 years old, brilliant and already prolific, and his assignment was among the most technically demanding aspects of the project.

It was important that someone like Sagan could accurately model the expansion of the dust cloud caused by a nuclear explosion on the Moon, so they could determine whether the explosion could be seen from Earth.

The team worked through 1958 and into early 1959. Reiffel produced multiple technical reports, and the project gained real momentum within the Air Force Special Weapons Center, its institutional sponsor.

At this point in the story, I want to address the question of what would actually happen if a nuclear weapon were detonated on the moon.

There are two things that make the moon different from the Earth for the purposes of this discussion. There is only one-sixth the gravity, and there is no atmosphere.

The most dramatic effects of a nuclear weapon on Earth, the blast wave, the fireball, and the mushroom cloud, all depend on the atmosphere. Mushroom clouds from a nuclear explosion are caused by the movement of dust and debris kicked up in the air. The Moon, however, is essentially a vacuum.

Without air to compress and superheat, there is no shock wave propagating outward from the explosion. The energy that on Earth would be transferred into a crushing wall of overpressure has nowhere to go in the conventional sense.

Similarly, without an atmosphere to ionize and superheat into an incandescent fireball, the visual signature of the explosion is dramatically different.

Instead of those familiar atmospheric effects, the energy of the detonation would be directed toward three things: intense radiation, vaporization of the surrounding lunar regolith, and ejection of surface material. The bomb and everything immediately around it would be instantly vaporized into superheated plasma.

That plasma would expand rapidly outward in all directions, not as a contained fireball, but as a rapidly dispersing cloud expanding into a vacuum. Without gravity to constrain it and without atmosphere to slow it, that ejecta cloud would travel enormous distances across the lunar surface, and some material might achieve escape velocity and be lost in space

The crater produced would depend on the weapon’s yield. The bomb envisioned for Project A119 was comparable in yield to the Hiroshima bomb, roughly 15 to 20 kilotons.

Given the Moon’s lower gravity and the lack of an atmosphere, the resulting crater would be significant but by astronomical standards unremarkable, roughly comparable in size to many naturally formed craters on the lunar surface.

The initial fallout from the blast would be significant for days to weeks; however, it would soon be overwhelmed by the background radiation from cosmic rays, which on the moon’s surface is 200x greater than on Earth’s. The Earth is protected by both its atmosphere and its magnetic field, and the moon is not.

The big question for the researchers at the time, and the entire purpose of the project, was whether you could actually see a detonation from Earth. This was the core question that Carl Sagan was tasked with. Reiffel and his team concluded that it could be faintly visible under the right conditions.

For example, if there was a crescent Moon and an explosion on the night side, visibility might be possible.

The key insight was that the most visible element would not be the instantaneous flash of the explosion itself, but the expanding dust cloud, which could be illuminated by sunlight for longer than the milliseconds of the primary burst. Placing the detonation along the terminator, as planned, would allow sunlight to catch the plume of ejected material against the dark background of the lunar night sky.

If the detonation was near the equator on a full moon, you probably couldn’t see it. I should note that meteors impact the surface of the moon all the time, many at higher energies than an atomic blast. Almost none of these have ever been observed by the naked eye.

Pretty much nothing would happen to the moon. There would be another relatively small crater on the surface, and that’s about it. It would not alter the Moon’s orbit in any measurable way.

The gravitational relationship between the Earth and Moon would have been entirely unaffected by a weapon whose energy output is a rounding error compared with the forces governing planetary mechanics.

The project was canceled in early 1959, for reasons that combined strategic, scientific, and practical concerns and made the plan untenable.

The most immediate concern was the risk of failure. The military leaders feared a negative public reaction to such a blast and that the missile could miss the Moon entirely, returning to an unknown location on Earth.

An intercontinental ballistic missile that missed the Moon and fell back toward a populated area would be catastrophic, militarily, diplomatically, and politically. The risk was not trivial.

Concern over serious damage to the Moon, as well as potential casualties on Earth if things went wrong, ultimately killed the program.

There was also the question of public perception. As the blast might have been visible to people on Earth, the Air Force decided the public might respond negatively to the militarism of the Moon.

The project remained deeply classified for nearly four decades. The existence of Project A119 was essentially unknown until the mid-1990s, when a Sagan biographer stumbled across classified details of the program in Sagan’s 1959 scholarship application to UC Berkeley’s Miller Institute.

By listing classified work in a fellowship application, Sagan had inadvertently created a paper trail that would eventually unravel the secret, though it would take decades for anyone to notice.

There is one interesting epilogue to the story.

In 2010, researchers were going through documents from the former Soviet Union. What they discovered is that the Soviets were, in fact, thinking about detonating a nuclear device on the moon, just like the Americans thought they were.

Oddly enough, they came to the same conclusion that the Americans did and decided not to do it.

Project A119 was one of the oddest moments of the Cold War. It wasn’t even so much about the proposal to nuke the moon itself that was odd, although that was odd. It was the desperation on the part of the Americans to do something, anything, to regain the status and prestige that they had lost with the launch of Sputnik.