“Project Orion was the first engineering design study of a spacecraft powered by nuclear pulse propulsion, an idea proposed first by Stanisław Ulam during 1947. The project, initiated in 1958, envisioned the explosion of atomic bombs behind the craft.
Each 0.15 kt of TNT blast would add 30 mph (50 km/h, 13 m/s) to the craft’s velocity. To reach low Earth orbit (300 mi), this sequence would have to be repeated about 800 times, like an atomic pogo stick. A preliminary design for the explosives was produced. The whole thing was built into a can with a diameter no larger than 6 inches (15 cm) and weighed just over 300 lb (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!).
Orion would have offered performance greater than the most advanced conventional or nuclear rocket engines now being studied. Cheap interplanetary travel was the goal of the Orion Project. Its supporters felt that it had potential for space travel, but it lost political approval over concerns with fallout from its propulsion. The Partial Test Ban Treaty of 1963 is generally acknowledged to have ended the project.”
Text bits from Wikipedia.