The launch of a Saturn V rocket is an impressive sight. It is impressively noisy, impressively big and impressively risky. It is also one of Man's outstanding examples of conspicuous consumption, where a few thousand tons of fuel go up (literally) in smoke (literally) in a couple of minutes. And yet it is, in 1979, the best space transportation system that we have. If we were to sit down and make a list of the properties of our 'ideal' space transportation system, without worrying about whether or not we could ever hope to achieve it, what would it look like? Well, first and most important it ought not to use up any raw materials in its working—no reaction mass, which all rockets need to propel themselves. It ought to allow us to take materials up and down from planetary surfaces, and be equally good at moving us around in free space. And it would be nice if it were somehow completely energy-free. While we are at it, let's ask that it be also silent and non-polluting. Note that our old friend, the rocket, satisfies none of our ideal system requirements.
