"It used a shaped-charge fusion-boosted fission explosive. The explosive was wrapped in a beryllium oxide "channel filler", which was surrounded by a uranium radiation mirror. The mirror and channel filler were open ended, and in this open end a flat plate of tungsten propellant was placed. The whole thing was built into a can with a diameter no larger than 6 inches (15 cm) and weighed just over 300 lbs (140 kg) so it could be handled by machinery scaled-up from a soft-drink vending machine (indeed, Coca-Cola was consulted on the design!)"
1960's Nuclear science was the best science. "We are going to make our propulsion system a scaled up vending machine that dispenses nuclear shaped charges and we are going to use it to blast an 8 million ton rocket to the moon!"
Ha, I've been re-watching Carl Sagan's Cosmos and this was described in detail as both the best possible application of nuclear bombs and a means to to reach, I believe Carl said, 1/20 the speed of light. Don't quote me on that fraction, but it was something surprising, albeit theoretical.
Freeman Dyson, working with Kurt G�del, suggested Orion could be used to travel back in time, if the universe rotates (which is a major plot point in a certain Neal Stephenson novel, SPOILERS)