Orion was the offspring of an idea first proposed by Los Alamos mathematician Stanislaw Ulam shortly after the Trinity atomic bomb test at Alamogordo, New Mexico. The idea was to have a spaceship propelled by a succession of nuclear explosions detonated behind the craft, propelling it forward. Each cycle would involve ejecting slow-moving propellant, igniting the bomb, and then bouncing some of the resulting fast-moving propellant off the bottom of the ship. For about one three-thousandth of a second the plasma stagnates against the pusher plate at a temperature of about 120,000 degrees. The time is too short for heat to penetrate the pusher, so the ship is able to survive an extended series of pulses.
Conceptually, the first two hundred explosions, fired at half-second intervals, with a total yield equivalent to some 100,000 tons of TNT, would lift the ship from sea level to 125,000 feet. Six hundred more explosions, gradually increasing in yield to 5 kilotons each, would loft the ship into a 300-mile orbit around the earth.
Stanislaw Ulam is on record as the principal inventor of space propulsion by nuclear bombs. The bombs would be detonated at a distance of some 50 meters from the base. Synchronized with this, disk-shaped masses of propellant would be ejected in such a way that the rocket-propellant distance would be about 10 meters at the instant the bomb blast hits it. The propellant is raised to high temperature and expands, transmitting momentum to the vehicle. With accelerations of the order of 10,000 g, it was recognized that the they would just crush a person into a blot.
Ulam considered the possibility that spacecraft could utilize gravitational energy for free in passing planetary bodies. However, it was felt that the computations required to plan changes in the trajectory would be of prohibitive length and complication with the computers available at that time.
General Atomics was founded in 1955 "for harnessing the power of nuclear technologies for the benefit of mankind". Physicists Edward Teller and Freeman Dyson were major players. One of the projects they looked at was controlled fusion, classified under the code name "Project Sherwood", which the author notes appeared closer in 1955 than it does today.
It was Edward Teller, according to Ted Taylor, who stood up and said: "What the world needs is a safe reactor." Not only idiot-proof, but Ph.D.-proof. Inherent safety "must be guaranteed by the laws of nature and not merely by the details of its engineering," Freeman explained. This resulted in the TRIGA (Training, Research, Isotopes, General Atomic) design, which is the only nuclear reactor design that has consistently turned a profit for forty years. To make TRIGA inherently safe required a prompt negative temperature coefficient, meaning that as soon as the reactor core starts heating up, the rate of fission immediately drops. This was done by incorporating hydrogen within the fuel, in the form of zirconium hydride.
Ted Taylor worked at General Atomic, focusing on making small fission bombs. He was able to design a fission bomb that you could hold in one hand that was about six inches in diameter. When Orion raised the possibility of using low-yield bombs for constructive purposes, it was a long-awaited opportunity for Ted.
In Quantum Electrodynamics (QED), Tomonaga, Schwinger, and Feynman had each arrived at the same physics but had taken different mathematical approaches. Freeman demonstrated the mathematical equivalence of the theories and presented a simpler method of applying the theory to specific problems. Freeman explained in 1953. "Some 10 or 20 qualitatively different quantum fields exist. Each fills the whole of space and has its own particular properties. There is nothing else except these fields; the whole of the material universe is built of them...". Freeman's methodology was key to analyzing the rearrangement of nuclei in the first few microseconds of the bomb's explosion.
Freeman: "In the early days of the project we were all amateurs. Everybody did a little of everything. There was no division of the staff into physicists and engineers. The ethos of engineering is very different from that of physics. A good physicist is a man with original ideas. A good engineer is a man who makes a design that works with as few original ideas as possible."
For the entire seven years of its existence, the project was plagued, politically, by the features that made it so appealing to people like Freeman and Ted. "Our military space program was unable to wholeheartedly adopt a project aimed at peacefully exploring the solar system. Our nonmilitary space program was unable to wholeheartedly adopt a project driven by bombs."
General Atomics headquarters included a 135 ft. fluted, toroidal library. There arose a realization that the Orion spacecraft would be about the size of the library. Taylor: "To me, the library always was Orion, ready to take off."
Testing of the concept took place at Point Loma, where a three-foot-diameter model of the device was flown. It weighed 270 pounds and used 2.3
lb charges. The main challenge was how to eject the bombs. In these tests, a series of high-explosive charges — grapefruit-sized balls of C-4, shaped by hand and cushioned by polystyrene foam inside coffee-can-sized canisters — were ejected through the middle of the pusher plate at quarter-second intervals from a central stack.
It was the need for 1,000 tons of pusher plate, as much as the desire for a 1,000-ton payload, that set the 4,000-ton benchmark for Orion's initial design.
Landing the mother ship on larger objects such as Mars or Ganymede, against gravity that was even one-third or one-sixth of Earth's, was risky, both because of the danger of crashing the ship and because the landing site would be contaminated by the last few bombs. While the compelling reason to land on a satellite would be to pick up propellant, the official mission at the beginning was just Mars. Departing Earth during a favorable outbound period, and then waiting on Mars for a favorable return, the numbers worked out as follows: Earth to Mars, 258 days; then a 454-day wait; Mars to Earth, 258 days; for a total of 970 days or 32 months.
For the Orion system, working at an effective exhaust velocity of 50 km/sec, these trips need mass ratios of 3.3 and 5.0 respectively. The mass ratio for an Apollo return trip to the Moon is about 600 to 1.
ARPA's sponsorship of Orion assigned interim management to the Air Force, while reserving a seat at the head of the table for NASA, expected to step in and take the lead once its mandate from Congress was defined. When NASA support for Orion failed to materialize, the Air Force assumed responsibility by default. Orion thoroughly examined for its military potential.
The shadow of atmospheric fallout had loomed over Orion from the start. Fallout had become a hot political topic in 1954. While boosting Orion vehicles above the atmosphere with chemical rockets reduces the immediate fallout, a significant fraction of fission products released anywhere in Earth's magnetosphere — not just within Earth's atmosphere — will slowly spiral in along magnetic field lines and eventually reach the ground. If you spread this radioactivity over the earth more or less uniformly and use a number of 10,000 person-rads per death, it worked out something like ten people would be killed per mission from Orion. For Freeman, that was a fatal flaw. The nuclear test ban treaty was the end of Orion.
The use of Orion technology to deflect an asteroid expected to hit the earth was examined. A "typical" chondritic asteroid 100 meters in diameter, weighing 14 million tons, with a closing speed of 25 km/sec, would threaten us with an impact yield of 1,000 megatons. The interceptor would be launched when the assailant is at a distance of 15 million km, or one week from impact, and would attempt to cause a deflection of 10,000 km to safely miss the earth. The time from launch to intercept is about five hours.
At the time of the publication of the book - 2002 - NASA had started reconsidering the Orion concept under the name External Pulsed Plasma Propulsion.