During the 1950's, a project was set up to study the posibility of a spacecraft powered by nuclear weapons. Though this might seem farcical, the physics are actually sound, and small scale models using conventional explosives actually flew. |Read More|
Project Orion was the first engineering design study of a spacecraft powered by nuclear pulse propulsion, an idea first proposed by Stanislaw Ulam in 1947. The project, initiated in 1958, was led by Ted Taylor at General Atomics and physicist Freeman Dyson, who at Taylor's request took a year away from Princeton's Institute for Advanced Study to work on the project.
The Orion design would have worked by dropping fission explosives out the rear of a vehicle, and catching the blast with a thick steel or aluminum pusher plate. Large multi-story high shock absorbers (pneumatic springs) were to have absorbed the impulse from the plasma wave as it hit the pusher plate, spreading the millisecond shock wave over several seconds and thus giving an acceptable ride. Low pressure gas bags were also proposed as a primary shock absorber. The two sets of shock absorption systems were tuned to different frequencies to avoid resonance. This sequence would be repeated thousands of times, like an atomic pogo stick.
The Orion nuclear pulse rocket design has extremely high performance, theoretically capable of obtaining a velocity of 3%–5% of the speed of light.
Missions that were proposed for an Orion vehicle in the original project included single stage (i.e., directly from Earth's surface) to Mars and back, and a trip to one of the moons of Saturn.
Another possible modern application for this technology would be to deflect an asteroid on a collison course with Earth. The extremely high performance would permit even a late launch to succeed, and the vehicle could effectively transfer a large amount of kinetic energy to the asteroid by simple impact. Also, an automated mission would eliminate the most problematic issues of the design: the shock absorbers.
SchematicsReaction mass for Orion would have been built into the bombs or dropped between 'pulses' to provide thrust. Reaction mass is required to transmit the force of the propulsion unit's detonation to the Orion's pusher plate, absorb neutrons and minimize fallout. Polyethylene masses, garbage and sewage were all considered for this purpose.
The Orion scientists built a series of models, called Put-Puts or Hot Rods, to test whether or not pusher plates made of aluminum could survive the momentary intense temperatures and pressures created by chemical explosives. Several models were destroyed, but a 100-meter flight in November 1959, propelled by six charges, was successful and demonstrated that impulsive flight could be stable. These experiments also proved that the plate should be thick in the middle and taper toward its edges for maximum strength with minimum weight.
One aspect of the proposed vessel seems counter-intuitive today: because of the force involved in the thermonuclear detonations and the need to absorb the energy without harm, massive vessel designs were actually more efficient. The smallest 4000 ton model planned for ground launch from Jackass Flats, Nevada had each blast add 50 km/h to the craft's velocity. A graphite based oil was to be sprayed on the pusher plate before each explosion to prevent ablation of the pusher plate.
The biggest design, the "super" Orion, would weigh 8 million tons and could easily be a city. In interviews, the designers contemplated the large ship as a possible interstellar ark. This extreme design could be built with materials and techniques that could be obtained in 1958 or were anticipated to be available shortly after.
The main unsolved problem for a launch from the surface of the Earth was nuclear fallout. Also the danger of damage to electronic systems on the ground from electromagnetic pulse, as well as flooding the van Allen belts with high-energy radiation. This problem might be solved by launching from very remote areas, because the EMP footprint would be only a few hundred miles wide. Assembling a pulse drive spacecraft in orbit by more conventional means and only activating its main drive at a safer distance would be a less destructive approach.
The vehicle and its test program would violate the Partial Test Ban Treaty of 1963 as currently written, which prohibits all nuclear detonations except those which were conducted underground. Adverse public reaction to any use of nuclear explosives is likely to remain a hindrance even if all practical and legal difficulties are overcome.
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