"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 Gödel, 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)