In the early days of the Atomic Era, American scientists were fascinated by the idea of sending an entire colony of humans to Mars using an engine propelling a ship with a series of controlled atomic bomb blasts behind the craft. They called the project Orion, after the constellation featuring man in the stars.
The project itself, led by physicists Ted Taylor and Freeman Dyson, began in 1958 at General Atomics and was ended only after the United States signed the Partial Nuclear Test Ban Treaty in 1963 with the Soviet Union and the United Kingdom.
Taylor was the leading nuclear weapons designer at Los Alamos. His idea for the Orion engine protected the capsule from the explosions by a large, flat "pusher plate," that was 1,ooo tons, 100 feet in diameter, and one foot thick.
The Orion project required a high-thrust and high efficiency impulse engine, expected to be gained from the nuclear explosions. Chemical-fueled engines of the time produced high thrust but had low efficiency. Electric ion engines are the opposite, producing low thrust, but are very efficient. Scientists felt the Orion engine provided the best opportunity for travel to another planet.
The bigger the rocket, the more fuel it needs to lift off. Many are mostly fuel tanks attached to a small ship. The ship would ride like a saucer, on top of the bomb's mushroom cloud. Atomic bombs give a million times more energy than rocket fuel. If a ship could survive the blast, it would be easy to lift it into space.
"The space exploration of those days was looking at the universe through a keyhole," Dyson said in an interview in the 1990s. "We wanted to open the door."
The size of the vehicle used would be directly proportionate to the bomb yields. The smallest proposed diameter was 17-20 meters in size with the largest having a mass of 8 million tons, the size of a small city.
Dyson's designs for the thermonuclear powered Orion proposed a top speed of 3-5 percent of light speed, which would require 44 years to reach Alpha Centauri, the nearest star system to our own.
In the earliest versions, scientists proposed the ship take off from the ground, causing significant nuclear fallout, radio active dust and ash blown into the atmosphere and left to fall back to Earth. Excessive fallout was one of the driving reasons for the signing of the Test Ban Treaty.