RogerBW's Blog

Project Orion, George Dyson 24 November 2016

2002 non-fiction: George Dyson, son of Freeman, recounts what can be told of the history of Project Orion, a plan to propel spacecraft with nuclear explosions.

A great deal of the work done for the project is still classified, which seems odd until you realise that it deals with the construction of shaped-blast nuclear explosives, and with building things that can stand up to the results. I certainly learned some practical details from this book, and I wasn't wholly ignorant of nuclear weapons design when I started.

The project's real problems were political, of course, but not the obvious politics: needing nuclear bombs meant there had to be military involvement, but the military couldn't readily come up with a use for a 4,000-ton manned spacecraft, especially once unmanned observation satellites and ICBMs become possible, and couldn't justify trips beyond the Moon. Meanwhile, NASA was very interested in exploring the solar system, but, well, nuclear bombs; indeed, one of the concerns about building small craft was that it would necessarily mean developing and building huge numbers of extremely reliable small nuclear weapons. As the USAF was gradually pushed out of any presence in space, chemical rockets just seemed more politically acceptable even if they had vastly inferior performance.

Fallout was a problem too, of course; in the glory days of atmospheric nuclear testing, a single launch wouldn't add much in proportion, but that was still a fair amount (probably about ten premature deaths' worth world-wide, to add to the thousand or so from other detonations). Mind you, the fallout is fairly constant per launch, since larger vehicles can use more efficient and cleaner bombs, which is an argument for some of the really massive concepts…

Because the project never got as far as an actual nuclear test – though miniature flight models running off high explosives showed the soundness of the basic concept – one doesn't know what other problems would have arisen. One of the major difficulties was clearly going to be getting the bombs reliably into place from ship to detonation area, with a blast rate of something like one per second: through a hole in the shock absorber? Round the edge (which lets you have multiple launchers), with a rocket to point it in the right direction before it goes off?

Orion does remain the only space drive in current theory, including all sorts of concepts involving fusion that certainly aren't buildable yet, that would produce both high thrust and high specific impulse.

But if you've ever wondered what the Manhattan Project guys did after the war, this is a big part of it. The original idea came from Stanislaw Ulam, for example; Feynman (who'd casually invented a NERVA-style reactor/hydrogen rocket concept) ran away at speed from what seemed at first as though it might be another all-out project like Manhattan. Bethe, Kantrowitz, and even von Braun were peripherally involved.

This is a pretty crunchy book which goes into engineering details, including the proposed armament of the military version: Casaba-Howitzer, a nuclear shaped charge firing a narrow jet of high-speed, low-density plasma, to be ejected from the craft and detonated while it was pointing at the enemy. You should know at least the basics of how nuclear weapons work before plunging in, though Wikipedia has sufficient information.

Dyson is not an inspiring writer, but the text flows well enough, even though the people often come over as a bit two-dimensional; for the most part their lives outside the project are dismissed in a few words. This is principally an account of the various directions research took, and secondarily of the efforts made to get a useful level of funding for the project.

An appendix lists the titles of the various papers written as part of the project (though in many cases they're still classified). Stability and Control of Space Vehicle. A Note on Maximum Opacity. Stability of Motion Induced by Blast. The Vapor-Pressures of Refractories and Their Fugacities Under Very High External Pressures. And… Betelgeuse.

You know, there's material for a 1950s space horror story right there.

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