Project Orion

Back in the late 1950s and early 1960s, the Mercury-Gemini-Apollo model for space exploration was not the only one under serious consideration.  How about a spaceship propelled by a series of focused nuclear blasts?  It might actually have worked, but there would have likely been a lot of fallout.  Literal fallout.  The concept was popular enough, though, to feature in a number of SF stories of the period. 

The original proposal was for travel within the solar system, but a version of the ship using antimatter could (at least theoretically) travel from 50 to 80 percent of light speed!

Links:

http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29
http://www.islandone.org/Propulsion/ProjectOrion.html