SpaceX

[MorningLightMountain]

the old Nuclear Bomb powered Orion:

the Orion design would have worked by dropping small shaped charge fission or thermonuclear explosives out the rear of a vehicle, detonating them 200 feet (60 m) out, and catching the blast with a thick steel or aluminum pusher plate.

http://en.wikipedia.org/wiki/Project_Orion_%28nuclear_propulsion%29

PS:

Jerry Pournelle, who is acquainted with the project and its ex-team leader Freeman Dyson, has been quoted as saying that a single mission could have provided us with a large permanent moon base. Alternatively, an Orion could reach Pluto and return to Earth inside of a year. In the early 1960s a NASA study proposed a rocket launched hybrid for a Mars round trip.