Crackpot Idea #454546 (Warning, involves rockets)First, a bit of background.
The recent re-emergence of commercial space flight and the US's plan to build a new heavy rocket have sparked a new wave of talk of the glorious, utopian future of space. Space stations, giant solar arrays, advanced materials, mining the asteroids, moon bases... The catch is, this has all happened before. The same thing came as a result of the roll-out of Apollo, something similar happened in the Soviet Union with the launch of the Energia rockets, and even, inexplicably, some of the same mania turned up with the launch of the Space Shuttle.
The big problem with space travel is rockets. A rocket of significant size uses most of its power lifting fuel, not the payload. Doubling the mass of a rocket will by no means double its payload. A Saturn V weighs 2,900 tonnes and has a payload of 118 tonnes to LEO; a Nova design which weighed over 50,000 tonnes had a payload of only 500 tonnes to LEO. The engineering challenges of building such large rockets are considerable, and most heavy rockets have a payload to LEO in the 25 tonne range; the Soviet/Russian Proton, the European Ariane V, the commercial Falcon 9 (under development) and the American Delta IV-H and Atlas V(Heavy) (both under development, though the Delta IV has been tested) are all in this range. So, it looks like lifting very heavy loads by chemical rocket is not an option.
What about nuclear? What indeed. In the early US and Soviet space programs, nuclear thermal rockets were developed; their efficiency was limited due to the rather low temperatures acheivable at the time without damaging the reactor, but they still beat chemical rockets by a wide margin. The top stage of the Saturn V was nearly a small nuclear device, and Werner Von Braun developed a single stage to orbit nuclear rocket capable of putting 500 tonnes in LEO. Nuclear rockets were tested on the ground, but by the time they were developed were politically unacceptable.
Then, there was Project Orion. Project Orion was a collabaration between General Atomics and DARPA in the 50s and 60s; it consisted of a metal disk with a payload on top, from which was dropped small nuclear bombs. It rode into space on the explosions. Designs went from 10,000 tonnes to orbit to 8 MEGAtonnes to orbit. In all, the 10,000 tonne version required about 10 megatonnes of nuclear explosives, though a lot of that energy was wasted. A mini version with chemical bombs was tested, and worked. Of course, this was completely politically unacceptable.
(Crackpot ideas temporarily withdrawn while I investigate patents.)