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blake8086 comments on Crazy Ideas Thread - Less Wrong
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If one were to build a cannon (say a large, thick pipe buried deep underground) and use a nuclear bomb as propellant, could they achieve anything interesting? For example, boost a first stage payload to orbit, or perhaps Earth escape velocity? The only prior art I know of for this is the Pascal-B nuclear test shot.
Nuclear space guns have been proposed. Aside from the manhole cover: http://nextbigfuture.com/2010/03/150-kiloton-nuclear-verne-gun.html http://nextbigfuture.com/2010/12/sea-based-launch-option-for-nuclear.html
(This appears in Hannu's Quantum Thief trilogy, incidentally.)
See Project Orion. It's motto was "Mars by 1965, Saturn by 1970."
That's not really related though. I'm asking "what if you build a gun with nukes as propellant?", not "what if you build a plane that rocket jumps through air/space?". The idea is to impart the highest fraction of a single bomb's energy onto a payload. Orion is pretty wasteful in terms of energy conversion.
Orion requires quite a few detonations, though; even with a massive craft (much of which is pusher plate and shock absorbers) to absorb the impact, you have to use fairly low-yield bombs and each only provides a relatively short period of thrust. You could possibly design something that takes higher yields (especially higher relative to the vehicle mass) that would survive reaching orbit on one detonation, but it would be subjected to extreme acceleration - the kind that would crush any satellite launched thus far - and I suspect there might be too much risk of tumbling given the non-uniformity of the atmosphere.
I don't think a working model of this would look much like a cannon. Nukes don't directly produce (much of) a shockwave; most of the shock comes from everything in the vicinity of the warhead absorbing a massive dose of prompt gamma and/or loose neutrons and suddenly deciding that all its atoms really need to be over there. So if you had a payload backed right against a nuke, even if it managed to survive the explosion, it wouldn't convert much of its power into velocity; Orion gets its power by vaporizing the outer layers of the pusher plate or a layer of reaction mass sprayed on it.
But it might be possible, nonetheless. The thing I have in mind might look something like a large chamber full of water with a nuke in the center of it, connected by some plumbing to the launch tube with the payload. Initiate the nuke, the water flashes into steam, the expanding steam drives the payload. Tricky part would be controlling the acceleration for a (relatively) smooth launch with minimal wasted energy.
(And, of course, you're left with a giant plume of radioactive steam that you still need to deal with.)
I think you would actually want to use hydrogen. It would essentially be a really powerful light gas gun.
As I understood it, the reaction mass for Orion comes from the chemical explosives used to implode the bomb. (The bomb design would be quite unusual, with several tons of explosives acting on a very small amount of plutonium).
There are better options if you want to go nuclear for propulsion. http://www.nasa.gov/pdf/718391main_Werka_2011_PhI_FFRE.pdf
It's not an unreasonable amount of mass to get into LEO, and so very elegant as a drive.
Both your barrel and your payload need to be able to survive being at the epicenter of a nuclear explosion. Spitting jets of molten metal into space isn't particularly useful.
See also space gun.
A variation - an acceleration chamber like a synchrotron (or other circular acceleration system), with a flick to release a payload towards space. not sure if it would be viable on something heavier than a particle, and what would happen. to the payload being stretched in various G-forces, or how high you would get. (not being up on my physics enough to say if it would be catastrophic or viable)
I think all you need to do to release the payload is to stop flicking it, so that part should be easy.
I guess,
so: