Helios (propulsion system)

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A precursor concept to the Orion project, Helios is a spacecraft propulsion system that postulated detonating small, 0.1 kiloton nuclear bombs into a chamber roughly 130 feet in diameter. Water would be injected into the chamber, super-heated by the explosion and expelled for thrust. Like Orion, it would have achieved constant acceleration through rapid "pulsed" operation.

This design would have yielded a specific impulse of about 1150 seconds (compared to a modern chemical rocket’s 450 seconds). However, a number of technical problems arose, most prominently how to keep the combustion chamber from exploding from the great pressures of the atomic detonations.

The Helios propulsion system was originally conceived by Freeman Dyson