From a 1963 Douglas report on ROMBUS, a sketch of a nuclear pulse propulsion system. While this was from the same report as the Douglas Orion shown previously, it’s a wholly different sort of engine. This time the pusher plate is curved, and coated with a thick layer of an ablative. With this system, the thrust comes not from the bomb vaporizing a blob of water, plastic, tungsten or some other propellant and hurling it at high speed at the plate… this time, propulsion comes from the radiant energy of the bomb vaporizing the ablative on the plate and causing a thin layer of it to essentially explode. This is not a good system… the number of pulses you can fire before you need to send out Space Man Third Class Timmy to go slap another layer of paint on the plate is limited, and since the energy of the bomb is distributed over a wide area, the temperature the material can get to – and thus the effective specific impulse – is far lower than the temperature of the conventional Orions propellant, which is packed right next to the bomb.
Additionally, this pusher plate does not have a hole in the center to shoot the bomb through. Instead, a large number of ill-defined “nuclear charge emitter assemblies” ring the thing. Since they need to be out of sight of the blast, they cannot shoot the bombs radially inward, just, at best, straight aft. The bombs themselves *must* be equipped with some sort of active guidance and propulsion system to shoot them inwards to a precise spot in space.
Just not a good design. And the report does not seem to discuss this particular concept any further; all other references are to a General Atomic-style Orion propulsion system. Thus this drawing may be a carryover from earlier Douglas work, before they were given data on the General Atomic design work. Or it might be something the art department just slapped together. My guess would be the former, however.
