The origins of Orion are linked inextricably to the development of the atomic bomb. Stanislaw Ulam and Frederick de Hoffman conducted the first serious investigation of atomic propulsion for space flight in 1944, while working on the Manhattan Project. Stanisław Ulam had realized that nuclear explosions could realistically be used for spacecraft propulsion, providing an effective means to address the technical difficulties involved in manned exploration of the solar system. In the 1954 during the Operation Castle nuclear test series at Bikini Atoll, a crucial experiment by Lew Allen proved that nuclear explosives could be used for propulsion. Two graphite-covered steel spheres were suspended near the test article for the Castle Bravo shot. After the explosion, they were found intact some distance away, proving that engineered structures could survive a nuclear fireball. Project Orion formally began at General Atomics in 1957. The program was led by Ted Taylor and physicist Freeman Dyson, who at Taylor's request took a year away from the Institute for Advanced Study in Princeton to work on the project. Previous research conducted under the Halo series examined the possibility of pulse-detonation drives using nuclear explosives – however the problem of containing the energy unleashed within an enclosed thrust-chamber proved insurmountable, but the work paved way for Project Orion -- a study of spacecraft propelled by directed nuclear pulse propulsion. Orion works by firing small shaped charge atomic shells (pulse units) to a detonation point 60 meters (200 feet) behind a heavy pusher-plate mounted on a multi-stage shock absorber system. Heat and blast are not problematic in this approach because no effort is made to contain the energy released by the blast. Orion offered high thrust and high specific impulse, at the same time – without the energy limitations imposed by other propulsion methods. Orion would have offered performance on the order of hundreds of times greater than the most advanced conventional or nuclear rocket engines – the efficiency and throw-weight of Orion stands unchallenged by any propulsion system currently within technological reach. As a heavy lifter Orion is unsurpassed -- Orion actually works better with heavier payloads because of the force involved in the thermonuclear detonations and the need to absorb the energy without harm, massive vessel designs are actually a requirement, Orion designs had crew compartments and storage areas that were several stories tall – Orion was capable of surface launching payloads well into a realm of weight reserved for Naval battleships, literally Orion could loft thousands of tons to orbit with ease. Large multi-level 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 down-stepping the initial 100g impulse to a range humans can withstand – the typical Orion would accelerate at about 4g’s. The long arm pistons proved one of the most difficult design features. 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. Numerous model flight tests (using conventional explosives) were conducted at Point Loma in 1959. On November 14, the one-meter model, called "Hot Rod" (or "putt-putt"), first flew using RDX (chemical explosives) in a controlled flight for 23 seconds to a height of 56 meters. Film of the tests has been transcribed to video and shown on the BBC TV program "To Mars by A-Bomb" in 2003 with comments by Freeman Dyson and Arthur C. Clarke. The model landed by parachute undamaged and is in the collection of the Smithsonian National Air and Space Museum. The 'base design' consisted of a 4,000 ton model planned for ground launch from Jackass Flats, Nevada. Each 0.15 kt of TNT (600 MJ) (sea-level yield) blast would add 30 mph (50 km/h, 13 m/s) to the craft's velocity. Graphite based oil would be sprayed on the pusher plate before each explosion to prevent ablation of the surface. To reach low Earth orbit (300 mi), this sequence would have to be repeated about 800 times, with higher yield charges (15 kt) to be used above 60 kilometers altitude. Reaction mass for Orion would have been built into the bombs or dropped between 'pulses' to provide thrust. Polyethylene masses and other materials were considered. At General Atomics the preliminary design for the explosives was produced. It used shaped-charge fission explosive. The explosive was wrapped in a beryllium oxide "channel filler", which was surrounded by a uranium radiation mirror. The mirror and channel filler were open ended, and in this open end a flat plate of tungsten propellant was placed. The whole thing was built into a can with a diameter no larger than 6 inches (15 cm) and weighed just over 300 lb (140 kg) so it could be handled by machinery scaled-up from the soft-drink vending industry (indeed, Coca-Cola was consulted on the design). The bombs had to be launched behind the pusher plate fast enough to explode 20 to 30 m beyond it every 1.1 seconds or so. Numerous proposals were investigated, from multiple guns poking over the edge of the pusher plate to rocket propelled bombs launched from 'roller coaster' tracks, however the final reference design used a simple gas gun to shoot the devices through a hole in the center of the pusher plate. Freeman Dyson describes deployment of the pulse-unit: The bomb is ejected via a gas-fired gun, passing through an aperture in the center of the pusher-plate. “When the nuclear device is exploded, the channel filler absorbs radiation emitted and rises to a high temperature. The radiation case serves to contain the energy released by the explosion so that more energy is absorbed by the channel filler. The high pressure achieved in the heated channel filler then drives a strong shock into the propellant, which vaporizes the propellant and drives it toward the pusher-plate.” Tungsten had been chosen for the propellant and beryllium oxide for the channel filler, and uranium for the radiation case. Tungsten, 2.5 times heavier than steel, allows for a very thin pancake, producing an optimally narrow jet. “The expansion of the bomb and the subsequent compression of the tungsten pancake take a few millionths of a second. During this time, the channel filler and the propellant absorb neutrons and X-rays emitted by the bomb. This reduces the shielding required to protect the Orion crew, and transforms much of the bombs output into kinetic energy that can be intercepted by the pusher-plate and used to propel the ship. The propellant slab, after being compressed to about one-quarter of its original thickness, expands as a cigar-shaped jet of plasma, moving at some 150 km/sec (300,000 mph) toward the ship. It takes 300 microseconds to complete the trip. During this time the propellant cools to about 10,000 degrees. Within another few hundred milliseconds the propellant cloud hits the pusher plate (or the advancing front of the reflected shockwave produced by the initial collision) and is suddenly recompressed. For less than a millisecond the stagnating propellant reaches a temperature of between 100,000 and 120,000 degrees – about ten times the temperature of the visible surface of the sun In space, without an atmosphere to produce a fireball, you get about a millisecond of intense white light as all of the kinetic energy is converted into heat.” From Project Orion, the true story of the atomic spaceship, by George Dyson, Henry Holt, 2002 The cigar shaped distribution profile and low density of the plasma reduces the instantaneous shock to the pusher plate. The pusher plate's thickness would decrease by about a factor of 6 from the center to the edge, so that the net velocity of the inner and outer parts of the plate are the same, even though the momentum transferred by the plasma increases from the center outwards. At low altitudes where the surrounding air is dense, gamma scattering could potentially harm the crew and a radiation refuge would be necessary anyway on long missions to survive solar flares. Radiation shielding effectiveness increases exponentially with shield thickness, so on ships with mass greater than a thousand tons, the structural bulk of the ship, its stores, and the mass of the bombs and propellant would provide more than adequate shielding for the crew. Stability was initially thought to be a problem due to inaccuracies in the placement of the bombs, but it was later shown that the effects would tend to cancel out. The first proposed shock absorber was merely a ring-shaped airbag. However, it was soon realized that, should an explosion fail, the 500 to 1000 ton pusher plate would tear away the airbag on the rebound. So a two-stage, detuned spring/piston shock absorber design was developed. On the reference design, the first stage mechanical absorber was tuned 4.5 times the pulse frequency whilst the second stage gas piston was tuned to 1/2 times the pulse frequency. This permitted timing tolerances of 10 ms in each explosion. The final design coped with bomb failure by overshooting and rebounding into a 'center' position. Thus, following a failure (and on initial ground launch) it would be necessary to start (or restart) the sequence with a lower yield device. In the 1950s methods of adjusting bomb yield were in their infancy and considerable thought was given to providing a means of 'swapping out' a standard yield bomb for a smaller yield one in a 2 or 3 second time frame (or to provide an alternative means of firing low yield bombs). These days the yield of a standard device would be 'tuned down', as needed, 'on the fly'. Had we built Orion in 1959 the world would be a vastly different place, it is likely we would have a thriving industrialized near-earth infrastructure and permanent bases on Mars. Our questions regarding the possibility of life during warmer and wetter times on Mars and the existence of life swimming in the lightless oceans beneath the icy frozen moons of Jupiter and Saturn might be a known fact. Orion stands as a monumental work of research that may one day pave the road for a far more expansive human presence in the solar system.

Wow

Awesome modeling, as usual. Corrie

Your modelling is, as usual, marvellous. Your accompanying article is a testiment to the far-sighted vision of the scientists involved, and an indictment of the myopic planet-bound view of the politicians concerned.

a fine piece of research, bud, and grand models!!

Excellent work! Great details, like the external ladder. Thanks for the mini-article that comes with it too.

fantastic image!

Top-notch modeling work, and as usual your research and practical physics surpasses the usual fare, supreme and very inspiring work!

EXCELLENT!