Dr. Jordin Kare has an interesting proposal for cheap space launch. Use lasers to remotely energize (zap a heat exchanger on) lightweight craft carrying hydrogen. The hydrogen wouldn't burn. Instead, it would just act as a reaction mass of very low weight, thus producing very high exhaust velocities. Basically, this would give you the exhaust velocity (read: fuel efficiency) of the upper theoretical end of nuclear rockets, but without the heavy nuclear equipment onboard, making the craft even lighter and more efficient.

But that's not even the clever bit. The clever bit of Jordin's proposal is that the laser tracking/energizing system can be built modularly. You can build one prototype module that can launch one toy craft. Then you figure out how to mass produce it and build a whole bunch of these puppies that can lock onto and zap a much larger heat-exchanger carrying craft.

What you get is very cheap access to orbit without ungodly huge R&D and infrastructure costs up front.

http://www.google.com/search?sourceid=chrome&ie=UTF-8...

(In this case "ungodly huge" = price of a space elevator.)