Physicists’ Early Dreams of Nuclear Powered Spaceflight

Physics

Considering how much space junk is in orbit, the need to maintain and monitor cislunar space (the region between Earth and the Moon) is becoming an increasingly important issue. To do so effectively may require spacecraft that can propel for longer durations than currently available, and nuclear reactors may offer a solution.

Recent news of progress utilizing nuclear technology to power extended spaceflight — from the Demonstration Rocket for Agile Cislunar Operations (DRACO) program, SpaceNukes, among others — is an opportunity to reexamine the history of this technology and pinpoint the origins of nuclear propulsion: Project Orion.


The Beginnings of Nuclear Propulsion

 At the end of World War II, after witnessing the catastrophic destruction possible from nuclear weapons, physicists actively sought peaceful applications of such nuclear capabilities. Nuclear power, once regarded as “too cheap to meter,” is a well-known example of these efforts, but some saw another opportunity: space travel. Polish mathematician Stanislaw Ulam, who worked on the Manhattan Project, undertook preliminary calculations as early as 1946. More than a decade of work at Los Alamos National Laboratory resulted in a co-authored 1955 report (and several reports thereafter) titled “On A Method of Propulsion of Projectiles By Means of External Nuclear Explosions: Part I.” Ulam’s idea for a spacecraft propelled by thousands of nuclear bombs was taking shape.

Soon after, Ted Taylor, America’s leading atomic bomb designer at the time (though staunchly against nuclear weapons), sold the idea of a nuclear propelled spacecraft to General Atomic (also jokingly referred to as “Generous Atomics” by some physicists due to their ample financial resources), and Project Orion began. Taylor knew Ulam through collaborative work at Los Alamos and described some of their conversations on fissile explosives in a 1995 oral history interview. Taylor recruited theoretical physicist and mathematician Freeman Dyson, who effectively joined to bolster the credibility of Orion. “If you just talked about the project, said you were going to propel a ship with nuclear bombs, the immediate reaction was that this was crazy. … They needed people with a solid reputation in order to have a chance to get the thing approved,” Dyson explained in the BBC documentary To Mars by A Bomb. Dyson, who dreamed of interstellar travel, handled rigorous calculations, from a proof-of-concept published in Physics Today showing nuclear propulsion was indeed a viable option to deriving the potential levels of radiation exposure per launch. (His son, historian of science George Dyson, authored a detailed account of Project Orion).

What kind of science fiction is this? (In fact, Stanley Kubrick considered using nuclear propulsion technology in the making of 2001: A Space Odyssey). Let’s see if we can convince ourselves otherwise. Or, for fun, just go give it a try on Kerbal Space Program. I’ll wait.

 


Project Orion Physics 101

 Project Orion engineers envisioned its design in a fundamentally different way than other approaches at the time; rather than focusing on meeting the minimum of what was physically permissible, why not go bigger? “Midrange” Orion would be several thousand tons, approximately the size of an ocean liner, and would hold a crew of 50 people. (The mass of “Super” Orion was estimated at 8 million tons, the size of a city!) Orion would be designed for round-trip missions to Mars, and even one-way trips all the way to Saturn.

Propelling an Orion vehicle demanded the systematic, controlled release of successive nuclear explosions. You could imagine the “nuclear pulse units” ejected one by one as if on an assembly line; in fact, Project Orion scientists consulted with the Coca-Cola company, thinking that the soft drink corporation’s machinery could be easily scaled up to handle the unit, which resembled a soda can (pictured below).

Diagram of an Orion nuclear pulse unit. Image Credit: NASA.
 

Diagram of an Orion nuclear pulse unit. Image Credit: NASA.

You might (quite reasonably) be wondering: if explosions occur so close to the ship, wouldn’t they cause damage? The Orion design incorporated a 1000-ton steel pusher plate mounted on shock absorbers smoothing the acceleration to levels that humans could withstand, between 2 to 4 g. However, there were two critical problems with the pusher plate: calculations predicted that the plate would ablate (erode) if unprotected from the repeated nuclear exposure and shockwaves from the blasts could cause spalling, or shards of metal breaking off.

 

Declassified footage from Project Orion testing. Video credit: U.S. National Archives.


Secrecy and Militarization 

The successful launch of Sputnik 1 in 1957 further amplified competition between the United States and Soviet Union amidst the ongoing space race. This urgency meant that the federal government was eager to find a fast and effective means of space travel. The newly formed National Aeronautics and Space Administration did not support Project Orion due to secrecy concerns due to its structure as a civilian space program.

The Air Force, however, agreed to contribute funding, but with another price. “Officially it had to be justified to the budgeteers as a military program, so they had to invent fake military requirements for it,” Dyson explained. The Air Force’s involvement with Project Orion, initially “a translation of a sword into a plowshare” and inspired by hopes of disentangling nuclear technology from its reliance on militarization, may have marked the beginning of its downfall. “Military influences were inevitably at work upon it.”

Eventually a car-sized model of the Orion spacecraft was constructed, and then-president John F. Kennedy visited the California site to see it in person. Managers had hoped that the presidential visit would help secure additional funding and political support, but Kennedy felt that the last thing the world needed was a nuclear weapons race in space, especially after the Cuban Missile Crisis. In August 1963, the international Limited Nuclear Test Ban Treaty was signed, effectively ending the Orion program.


“Death of A Project” 

In 1965, Dyson published an essay in Science titled “Death of a Project,” attributing the demise of Project Orion to the Defense Department, leaders of NASA, advocates of the Nuclear Test Ban Treaty, and “the scientific community as a whole.” “The story of Orion is significant because this is the first time in modern history that a major expansion of human technology has been suppressed for political reasons,” he wrote.

Despite the soundness of the science, Project Orion was morally difficult for many to get behind. “The idea isn’t crazy; the idea that we might do it is crazy,” physicist and author Arthur C. Clarke said of Project Orion. It’s a confluence of tight-lipped secrecy in a context of increasing anti-nuclear sentiment that didn’t exactly rally widespread support.

Johndale Solem, the former Los Alamos theoretical physicist, offered a succinct summarization: “Generally, people recoil from the notion of using nuclear explosives. I do; I recoil from that notion. Because I know we don’t have that kind of world. And I know that having nuclear weapons in space is inviting someone to misuse them.” Indeed, Project Orion is an important reminder that scientific justifications may not inherently prove sufficient plausibility; what can be done might not be done. Nevertheless, physicists dreamed of expanding humanity’s reach for the cosmos and sought worlds beyond our own, limited and seemingly clouded in destruction. In some ways, this sentiment still rings true today.

Artist’s conception of a Project Orion spaceship. Image credit: NASA

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