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podcast transcript
At the height of the Cold War, the United States considered a plan so bold it sounded like science fiction. That would be detonating a nuclear weapon on the moon.
Known as Project A119, the idea was born out of fear, prestige, and an urgent need for the Soviet Union’s nascent leadership in space.
The plan was real, the scientists involved were some of the most notable of the 20th century, and the implications were enormous.
Learn more about Project A119 and the quest for lunar nuclear weapons in this episode of Everything Everywhere Daily.
To understand Project A119 and what made people want to drop a nuke on the moon, you must first understand the mood of near-panic that gripped America in the fall 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. The tiny, beeping aluminum sphere, roughly the size of a beach ball, shattered assumptions about America’s technological superiority and sparked dire strategic implications. If the Soviet Union could put a satellite into orbit, it could deliver a nuclear warhead anywhere on the planet.
In this environment of anxiety and fear, someone in the United States Air Force asked a question that in any other era would have seemed crazy. 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 revealed to a U.S. Secret Service agent that the Soviet Union was planning to commemorate the anniversary of the October Revolution by detonating a nuclear weapon on the moon to coincide with the lunar eclipse on November 7.
It was unclear at the time whether this rumor was real or Soviet disinformation, but it reinforced the idea that the Moon would soon become a theater of the Cold War.
The intellectual foundations for thinking about nuclear explosions in space have already been laid. In February 1957, Edward Teller, the ‘father of the hydrogen bomb’, proposed detonating a nuclear device on and at some distance from the lunar surface to analyze the effects of the explosion.
The Armor Research Foundation (ARF), based at the Illinois Institute of Technology in Chicago, has been conducting exactly this kind of research for several years. ARF began studying the environmental effects of nuclear explosions in 1949, and became the home for such research in 1958.
Project A119 was a top secret project developed by the U.S. Air Force in 1958. The name was deliberately plain. It was the kind of bureaucratic title designed to be forgotten in a filing cabinet. However, the content of the plan was anything but ordinary.
In 1958, Dr. Leonard Reiffel, who worked at the Armor Research Foundation, was asked by the Air Force to “rapidly advance” research into what a nuclear explosion would look like on the Moon.
Reiffel was born in Chicago in 1927 and worked at the University of Chicago with Enrico Fermi, who created the first nuclear reactor. He was rigorous, cautious and politically savvy enough to understand what was really required of him.
The plan is presented in a paper titled “Study of Lunar Research Flights – Volume 1” and describes the following scenario: A hydrogen bomb would be too heavy for the mission, so the U.S. Air Force would launch a rocket carrying an atomic fission bomb to the moon, and once it reached the moon, it would avoid a crater and explode.
There were two layers to this project. The surface layer was scientific. The explosion could reveal useful information about the moon’s geology and composition through patterns of ejecta and seismic activity. But the deeper purpose was purely psychological and political. The Air Force wanted to surprise the Soviet Union and the world by saying, “Hey, look what we can do. We can blow up the moon.”
A visible explosion on the lunar surface, visible to millions of people around the world without the aid of a telescope, is a declaration of America’s technological prowess in the most dramatic terms imaginable.
The subjects were carefully selected. The explosions were supposed to occur strategically along the Terminator Line, the boundary between the bright and dark sides of the moon. This was no accidental choice. Explosions along the Terminator are illuminated by the Sun at a low angle, maximizing the visibility of the expanding dust cloud in the darkness of a moonlit night.
A team of 10 people, led by Leonard Reiffel, gathered at the Illinois Institute of Technology in Chicago to study the potential visibility of the explosion, its benefits to science and its impact on the lunar surface.
Among its members was Gerard Kuiper, one of the most outstanding planetary scientists of the 20th century. He was the man who would eventually give his name to the Kuiper Belt, the icy mass beyond Neptune. His presence on the team provided scientific credibility. But perhaps his most important contribution was his recommendation to bring in a particular graduate student, Carl Sagan.
Carl Sagan was a graduate student who modeled how clouds of gas and dust expand in low gravity. Sagan was only 24 years old, smart and already accomplished, and his task was one of the most technically demanding aspects of the project.
It was important for someone like Sagan to accurately model the expansion of the dust cloud resulting from a nuclear explosion on the Moon to determine whether the explosion would be visible from Earth.
The team worked from 1958 to early 1959. Reiffel authored several technical reports, and the project gained substantial momentum within its institutional sponsor, the Air Force Special Weapons Center.
At this point in the story I want to address the question of what would actually happen if a nuclear weapon were to explode on the moon.
For the purposes of this discussion, there are two ways in which the Moon differs from Earth. Gravity is only one-sixth and there is no atmosphere.
The most dramatic effects nuclear weapons have on Earth – blast waves, fireballs, mushroom clouds – all depend on the atmosphere. Mushroom clouds from nuclear explosions are caused by the movement of dust and debris in the air. But the moon is essentially a vacuum.
With no air to compress and superheat, there are no shock waves to propagate outwards from the explosion. The energy that would be transferred to the wall of overpressure on Earth has nowhere to go in the traditional sense.
Likewise, without the atmosphere ionizing and superheating into an incandescent fireball, the visual characteristics of an explosion are dramatically different.
Instead of these familiar atmospheric effects, the energy of the explosion is directed in three directions: intense radiation, vaporization of the surrounding lunar regolith, and ejection of surface material. The bomb and everything around it will be instantly vaporized into superheated plasma.
The plasma will rapidly expand outward in all directions, expanding into the vacuum, not as a contained fireball but as a rapidly dispersing cloud. Without gravity to limit it and an atmosphere to slow it down, the ejecta cloud would travel enormous distances across the lunar surface, and some of the material could reach escape velocity and disappear from space.
The crater created depends on the weapon’s production capacity. The bomb envisioned for Project A119 was similar to the Hiroshima bomb, with a yield of approximately 15 to 20 kilotons.
Given the Moon’s low gravity and lack of atmosphere, the craters created would be significant, but unremarkable by astronomical standards, and would be roughly comparable in size to many naturally formed craters on the lunar surface.
The initial fallout from the explosion will be significant for days to weeks. However, cosmic rays on the Moon’s surface are 200 times greater than on the Earth’s surface. The Earth is protected by an atmosphere and magnetic field, but the Moon is not.
At the time, the biggest question for researchers and the overall purpose of the project was whether the explosion would actually be visible from Earth. This was Carl Sagan’s central question. Reiffel and his team concluded that, under the right conditions, they can be faintly visible.
For example, if an explosion occurs at night during a crescent moon, visibility may be possible.
The key insight is that the most visible element is not the momentary flash of the explosion itself, but the expanding dust cloud that can be illuminated by sunlight for longer than the milliseconds of the primary explosion. If the explosion is placed along the terminator as planned, sunlight will be able to capture the plume of ejected material against the dark background of the lunar night sky.
If the explosion occurred near the equator of the full moon, it probably wouldn’t have been visible. It is important to note that meteors always impact the lunar surface, and in many cases they do so with higher energies than an atomic explosion. Almost none of these have ever been observed with the naked eye.
Nothing will happen on the moon. There will be another relatively small crater on the surface and that’s it. It doesn’t change the moon’s orbit in any measurable way.
The gravitational relationship between the Earth and the Moon would have been completely unaffected by the weapon, whose energy output would have been a rounding error compared to the forces that govern planetary dynamics.
The project was canceled in early 1959 because a combination of strategic, scientific, and practical problems made the plan unsustainable.
The most pressing concern was the risk of failure. Military leaders feared a negative public reaction to such an explosion and that the missile could miss the moon entirely and return to an unknown location on Earth.
An intercontinental ballistic missile that missed the moon and landed in a populated area would be a military, diplomatic, and political disaster. The risk was not trivial.
The program was eventually halted due to concerns about serious damage to the Moon and potential damage to Earth if something went wrong.
There was also the issue of public perception. Because the explosions would have been visible to people on Earth, the Air Force reasoned that the public might react negatively to lunar militarism.
The project was kept deeply secret for nearly 40 years. The existence of Project A119 was essentially unknown until the mid-1990s. Sagan’s biographer at the time stumbled upon confidential details of the program in 1959 when Sagan applied for a scholarship to the Miller Institute at UC Berkeley.
By listing confidential work on his fellowship application, Sagan inadvertently created a paper trail that would uncover secrets that would take decades for anyone to notice.
This story has an interesting epilogue.
In 2010, researchers were examining documents from the former Soviet Union. What they discovered was that the Soviets were in fact thinking about detonating a nuclear device on the moon, just as the Americans had thought.
Oddly enough, they came to the same conclusion that the Americans did, and decided not to.
Project A119 was one of the strangest moments of the Cold War. The proposal to drop a nuke on the moon itself wasn’t strange, but it was. Such was the desperation of Americans that they would do anything, anything, to regain the status and prestige they had lost with the launch of Sputnik.
