TCS Daily

The Road Not Taken (Yet)

By Glenn Harlan Reynolds - September 11, 2002 12:00 AM

In the old science-fiction movies, spaceships looked like, well, ships. They had massive steel girders, thick bulkheads, and rivets everywhere. And big crews, with bunks, staterooms, and mess halls. Now we know better of course: spaceships aren't big, massive constructions made of steel. They're cramped gossamer contraptions of composites and exotic alloys designed to keep the weight down.

It might have turned out differently. In his recent book, Project Orion: The True Story of the Atomic Spaceship, George Dyson tells the story of an engineering effort that, but for a treaty or two and a lot of bureaucratic infighting, might have given us spaceships like that. And the Solar System.

Orion was a nuclear-propelled spaceship. And by "propelled," I mean propelled. The idea - which sounds strange but turned out to look pretty practical - was to propel a spaceship by means of nuclear explosions. Bombs, of a sort, though specially constructed and low in yield, from less than a kiloton to a couple of kilotons. The bombs would be ejected and explode a few dozen meters behind a large pusher plate. The plate would absorb much of the blast, convert it to momentum, and transfer that momentum to the rest of the ship via a system of shock absorbers.

It's not terribly surprising, of course, that if you set off a nuclear explosion next to a large object, the object in question will move. The surprising discovery was that you could do that without destroying it at the same time. But experiments demonstrated that properly treated substances could survive intact within a few meters of an atomic explosion, protected from vaporization by a thin layer of stagnating plasma. (In addition, the 1957 Pascal-B underground nuclear test accidentally launched a manhole cover at speeds that may have exceeded escape velocity, though it isn't clear whether Orion researchers knew about this. The story of this test, often misnamed "Operation Thunderwell," which was actually the name of another nuclear-spacecraft project, has sparked many Internet legends.) The original idea had been Stanislaw Ulam's in 1948, but beginning in 1958 physicists Ted Taylor and Freeman Dyson (author George Dyson's father) worked with numerous other scientists and engineers to design a 4,000-ton spacecraft that would take advantage of this fact to extract motive force from atomic explosions. And, yes, I really did write 4,000 tons: Orion was big, clunky, and mechanical - featuring springs, hydraulic shock absorbers, and other 19th-century-style accoutrements. To handle the shock, it needed to be big. It probably would have had rivets.

TCS Video: Project Orion (NASA)
In fact, one of the greatest appeals of Orion was that the bigger you made it, the better it worked. While chemical rockets scale badly - with big ones much harder to build than small ones - Orion was just the opposite. That meant that large spacecraft, capable of long missions, were not merely possible, but actually easier, for a variety of reasons, than small ones. Bigger spaceships meant more mass for absorbing radiation and shock, more room to store fuel, and so on. As Freeman Dyson wrote in an early design study from 1959:

The general conclusion of the analysis is that ships able to take off from the ground and escape from the Earth's gravitational field are feasible with total masses ranging from a few hundred to a few million tons. The payloads also range from zero to a few million tons.
The appeal of the project was such that its unofficial motto became "Saturn by 1970," and those working on it believed that they would be able to build a ship capable of exploring the outer planets - indeed, capable of crossing the solar system in mere months - in time to make that trip. And why not? America was already very good at building atomic bombs, and had plenty of them. The other design problems (chiefly involving resonances in the pusher plate against which the nuclear shock wave struck, and in the shock-absorption system coupling the plate to the rest of the ship) were genuine, but they were mechanical engineering problems more akin to those involved in locomotive design than rocket science. In many ways, Orion was the ultimate "Big Dumb Booster."

The scientists and engineers who worked on Orion were confident. As one says:
It was dead serious. If we wanted to do it, if there were any good reason for wanting to have high specific impulse and high thrust at the same time, we could go out and build Orion right now. And I think it would make a lot of sense.
But it didn't happen, of course.

There were several problems. One was the 1963 Limited Test Ban Treaty, which forbids nuclear explosions in the atmosphere and in outer space. As Dyson makes clear, the United States might well have negotiated an exception to the treaty for projects like Orion, but chose not to. The reason it chose not to was that the United States was already committed to a chemical-rocket path to the Moon, and NASA was uninterested in other big projects - while the Air Force, another potential sponsor, couldn't come up with any plausible military reasons for 4,000-ton interplanetary spacecraft. (There were some halfhearted efforts by space enthusiasts within the USAF to come up with such missions, which led to President Kennedy being deeply unimpressed by a more-than-man-sized model of an Orion-powered "space battleship," but no one was fooled.) And this bureaucratic warfare was the other problem. Orion lacked a sufficient constituency, and it threatened too many people's rice bowls.

So what about now? Could Orion ever come back? The answer is yes. The Test Ban Treaty is a real obstacle to any future deployment of Orion. However, it binds only a few nations, and many nations (like India and China) that are both nuclear-capable and interested in outer space have never signed it. For an up-and-coming country looking to seize the high ground in space in a hurry, Orion could have considerable appeal. And, of course, even the United States could withdraw from the Treaty, on three months' notice, under the Treaty's own terms.

Orion's scientists weren't worried about fallout. Orion would have produced some, but the amount would have been tiny compared to what was being released already from above-ground tests, and there was hope that additional work would have produced even cleaner bombs designed specifically for propulsion. Today, people are much more nervous about radiation and under current political conditions a ground-launched Orion is a non-starter, at least in Western countries. But not everyone cares as much about radiation, and indeed the countries that worry about it the least are those most likely to find Orion appealing as a way to attain space supremacy over more established space powers in a hurry. What's "Orion" in Chinese?

Some have suggested that the 1967 Outer Space Treaty, which forbids placing "nuclear weapons or any other kinds of weapons of mass destruction" in outer space, would also be a barrier to Orion, but I don't think so. A nuclear "bomb" used for space travel, arguably, isn't a "weapon." It's a tool - just as the Atlas rockets that launched the Mercury astronauts were, because of their use, different from the otherwise identical Atlas missiles aimed at the Soviet Union. (When asked about the difference, Kennedy responded: "attitude.")

The technical data from Orion are still around (in fact, much of the design software is still in use, applied to other military and nuclear projects). Dyson's book contains a large technical appendix, listing much declassified information. Much other information is still classified, even after nearly forty years, but still in existence. Will Orion come to pass in the 21st Century? I wouldn't bet against it. Hmm. Saturn by 2020?

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