Whenever I think about Project Orion, I recall the ‘putt-putt’ experiments that tested the propulsion concept back in 1959. It was hardly an atomic spaceship, but the little putt-putt called ‘Hot Rod’ is as far as Orion ever got operationally. Using chemical explosives, Hot Rod rose 100 meters, a brief flight that nonetheless validated the idea that a spacecraft built around nuclear bombs, propellant and a pusher plate could be made to take stable flight.
An atomic spaceship. There was a time when the idea seemed to have interstellar possibilities. Freeman Dyson, a key figure in Orion, envisioned one version that used a copper pusher plate twenty kilometers in diameter. Driving the ship would be a nuclear arsenal of staggering proportions: 30 million nuclear bombs, each of which would explode 120 kilometers behind the vehicle at intervals of 1,000 seconds.
With a total acceleration time of five hundred years—and a comparable time for deceleration—this mammoth super-Orion would carry a colony of 20,000 Earth people to Alpha Centauri. Flight time: 1,800 years, making it a true multi-generation ship, where the distant descendants of the initial crew arrive at the target to make a new start for humanity. Later Dyson would ponder a pared down version that used 300,000 bombs to reach a final velocity of 10,000 kilometers per second, with arrival at Alpha Centauri in 130 years.
These days Project Orion’s interstellar capabilities seem vastly over-rated, even though its potential for travel to the outer Solar System was very real. Dyson himself now considers nuclear options unviable for missions to another star. When I was researching my book, I asked him his current views about Orion as a way to reach Alpha Centauri. Here’s a bit of what he said:
The Orion idea was exciting, but as far as interstellar trips are concerned, nuclear energy just doesn’t cut it… Youre using less than one percent of the mass with any kind of nuclear reaction whether it’s fission or fusion. The velocities you get are limited to much less than a tenth of lightspeed. Nuclear methods are great inside the solar system but not outside; in interstellar terms, they are not very interesting.
But what a story, and if you haven’t read George Dyson’s book about his father’s work, you’re missing out on a great experience. It’s Project Orion: The True Story of the Atomic Spaceship (New York: Henry Holt & Co., 2002). Online, the ever-reliable Anthony Kendall offers up a fine account of Orion. Here Kendall describes the vehicle, which would have dwarfed any rocket ever made:
A full-size Orion vehicle would have had a mass of 4,000 tons – about 40 times that of the Space Shuttle – and would include a “pusher plate” about 1-meter thick at the center. This solid mass of metal served to reflect the Orion craft away from the nuclear explosions, while at the same time protecting the passengers from the neutron radiation. The enormous shock absorbers between the pusher plate and the crew module would then distribute the 10,000 G’s of each nuclear blast to something much more comfortable for Orion’s passengers. In fact, an Orion launch would probably be much more comfortable than a conventional chemical rocket because of the sheer mass of the vehicle.
So vast were some Orion concepts that Ted Taylor, a weapons designer who became a guiding force behind the project, once considered installing a 4000-lb barber’s chair on the ship, thumbing his nose at the piddling chemical rocket designs that measured out payload in teaspoons. But of course, those chemical payloads got larger even as political currents made the nuclear option less realistic. The nuclear test ban treaty was but one of many blows that put an end to the program. Dyson talks about all this in Disturbing the Universe (New York: Harper and Row, 1979).
Be sure to read Kendall’s account for the overview, then George Dyson’s book, a volume I could hardly put down. And if you want to follow some of the interstellar references, start with Freeman Dyson’s paper “Interstellar Transport,” in Physics Today (October, 1968), pp. 41-45. The drama of Orion’s demise is told in Dyson’s “Death of a Project: Research Is Stopped on a System of Space Propulsion Which Broke All the Rules of the Political Game,” Science 149, No. 3680 (July 9, 1965), p. 141. And keep an eye on an Orion descendant called External Pulsed Plasma Propulsion, which may have much to teach us still.