|A "small" Project Orion ship|
But first, a little history:
Sponsored by the U.S. Government, Project Orion dates back all the way to the late 1940's and officially began in 1958. The idea was to explode nuclear devices behind a space ship and ride the shock wave forward. 800 atomic blasts later, and you've ridden an atomic hop ball into orbit. Keep it up and you could even get to Pluto and back in under a year - if you managed to stay in one piece.