Model: Orion. Orbital launch vehicle. Other Family: Cancelled. Country: USA. Status: Cancelled 1965.
Nuclear-pulse drive launch vehicle seriously developed by General Atomics in the United States from 1955-1965. The design allowed vast payloads of hundreds of tons to be hurled to the planets. By 1958 the Orion team saw themselves in direct competition with Von Braun’s chemical rockets. They hoped to a land a huge manned expedition on Mars by 1964 and tour the moons of Saturn by 1970. However politically NASA would not argue for the exception to the 1963 Nuclear Test Ban Treaty necessary to allow firing of nuclear explosions in space.
Zis is not nuts, zis is super-nuts
- Mathematician Richard Courant on viewing an Orion test
The nuclear pulse drive was conceived of H-bomb designers Stanislaw Ulam and Cornelius Everett at Los Alamos in 1955. Ted Taylor at Los Alamos further developed the concept. By the winter of 1957 Turner was working at General Atomics after developing the Triga small research reactor design with Freeman Dyson. Dyson managed to take a one-year sabbatical from his post at Princeton in order to work with Taylor on development of the nuclear pulse design at Los Alamos in 1958.
The nuclear pulse design, dubbed Orion, was a counter-intuitive approach to using the huge potential of nuclear energy for spacecraft propulsion without the costly development required for nuclear thermal or nuclear electric systems. Atomic bombs would be ejected aft of the rocket and exploded some distance away. Propellant (water or wax) surrounding the bombs would be transformed into high-energy plasma and bounce off a pusher plate at the rear of the rocket and push it forward. Shock absorbers would even out the ride. Although the plasma from the explosion would have a temperature of 80,000 deg K, the impulse would be brief and only a tiny layer of the ablative pusher plate would sublimate after each explosion. A method was developed of 'greasing' the plate between explosions to protect it.
Two shock absorber designs were explored. The first consisted of three donut-shaped gas-filled cushions, each one meter high, looking like a stack of tires. Six-meter high aluminium pistons rose from these absorbers. This system would limit peak G forces to 3 to 4 G’s. But it would be a bumpy ride for the passengers. Therefore the second design was more complex but allowed the shock absorbers to operate in synchronisation in order to further even out the G-forces. This would limit peak forces to 1.5 to 2.0 G’s.
The design allowed vast payloads to be hurled to the planets. A typical design had a payload of hundreds of tonnes, meaning no high-tech environmental recycling systems or lightweight structures or equipment would be needed. The pusher plate was typically about one third of the weight of the craft. The General Atomics team saw themselves in the post-Sputnik period as in direct competition with Von Braun’s chemical rockets. Dyson and the other believers thought they could land a huge manned expedition on Mars by 1964 and tour the moons of Saturn by 1970. Dyson particularly was anxious to bypass Mars and explore the moons of Jupiter and Saturn. They hoped to make these trips personally, in their lifetime.
Briane Dunne, the head of hardware development for the project, was less optimistic. He believed a practical design would not be ready until 2010-2050.
In the summer of 1959 Von Braun won the competition for selection of chemical or nuclear pulse rockets for use in the space program in the immediate future. The project was moved to the US Air Force, but the Air Force was not interested. Nevertheless the project struggled along for six years. Von Braun had enthusiasm for the design for use in Mars expeditions. A single launch of a Saturn V could orbit an Orion spacecraft that could take an expedition to Mars and back, whereas nuclear thermal or chemical designs would take 6 to 12. Therefore the General Atomics team later designed increasingly detailed but smaller and more limited designs for this approach. But Von Braun could not convince the NASA hierarchy of the scheme. It would put NASA in the position of arguing for an exception to the 1963 Nuclear Test Ban Treaty to allow firing of nuclear explosions in space. Finally funding was deleted entirely in 1965.
As a lark, at the end of the project, Dyson designed and published his theoretical designs for the ultimate nuclear pulse spacecraft - a starship. The pusher plate would be kilometres in diameter, and one megaton H-bombs would be ignited several kilometres behind the plate to propel it. Accelerations would be low, so the light structure would have to be built in space. Two versions were proposed, but even the faster model would only allow the grandchildren of the participants to reach Alpha Centauri.
Manufacturer: General Atomic.
Model: Orion Test Article.
The original test article for Project Orion had a total mass of 133 kg including its bullet-shaped outer shell.
Six charges, each with 1.04 kg of C4 high explosive, were ejected from the rear of the pusher plate and exploded 866 mm behind the plate. An initial charge of 452 kg of gunpowder in a mortar-like launch cylinder got the craft going. The original article was too heavy to accelerate after running out of momentum from the original charge.
The baseline planetary version of Orion would have launched from the earth's surface. It would have been bullet-shaped, 41 m in diameter and about 50 m high.
Launch would have been from the Atomic Energy Commission test site at Jackass Flats, Nevada. Initially 0.1 kiloton bombs would have been exploded behind the pusher plate at one second intervals. Once clear of the earth's atmosphere and radiation belts this would gradually increase until 20 kiloton bombs would be ignited every ten seconds. The 10,000 tonne ship would hold 2000 bombs and have a net payload of several thousand tonnes, sufficient to house a crew of 150 in comfort.
The rocket would have had an exhaust velocity of 3000 seconds and be able to make the round trip to Mars in two years. Jupiter or Saturn would take only three years round trip. On a Jupiter voyage the approach velocity would be 67 km/sec and the braking manoeuvre would take only 1000 seconds. The voyage could be made even shorter if the ship would refuel with propellant at Callisto - water or frozen methane or almost any available ice could be used.
The final iteration of the Orion design was a nuclear pulse propulsion module launched into earth orbit by a Saturn V. The 100 tonne unit would have had a diameter of 10 m to match that of the booster. This would limit specific impulse to 1800 to 2500 seconds, still two to three times that of a nuclear thermal system.
A second launch would put a 100 tonne Mars spacecraft with a crew of eight into orbit. After rendezvous and checkout, the combined 200 tonne spacecraft would set out on a round trip to the Mars - total mission duration as little as 125 days!
