Physicists’ Early Dreams of Nuclear Powered Spaceflight

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

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.

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 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” 

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.