At first, nuclear bombs such as atomic bombs were only used for war such as the bombings of Hiroshima and Nagasaki in August 1945. Some people wanted to use nuclear explosives for peaceful purposes. In the 1950s General Atomic was started and this was a time when nuclear weapons were kept top secret.
In 1958 a team of 19 scientists headed by Theodore Taylor started a top secret space project in an attempt to develop an atomic spaceship propelled by nuclear explosives behind a pusher plate cushioned by duel shock absorbers and shock-absorbing columns. Since not only did they intend to use it for interplanetary travel but also to eventually go to the stars they named it Project Orion after a famous constellation. One key participant of Project Orion was the physicist Freeman Dyson. The hope was to have cheaper ways of exploring deep space than chemical rockets. Nuclear bombs provide a million times more push than chemical rocket combustion. Plus chemical rockets are limited to carrying small manned payloads such as capsules while a nuclear bomb-propelled Orion could take big payload with many times more bang for your buck.
No actual spacecraft emerged from Project Orion during its first life or to this day yet, but there were multiple small flight test vehicles some of which were damaged or destroyed. The first successful flight test vehicle first flew on 1959 and rose to an altitude of tens of meters as high as Orion would ever go in its first life. The flight test vehicles used chemical explosives.
Starting as early as 1960, Orion began to lose both momentum and support from Washington. The attitude at the time was that they could make do with chemical rockets. A video of Project Orion was shown to Werner Von Braun but it was too little too late. That was because Orion was kept top secret and NASA likes to be as open as possible. But a bigger problem was the radioactive fallout that would result from the nuclear explosions that would propel an Orion spacecraft. In 1963, the United States, the Soviet Union, and Great Britain signed the Nuclear Test Ban Treaty which forbids nuclear weapons explosions in space. So before there could be any Orion prototypes using nuclear explosives, the project was put to bed in 1965.
But since Orion was shut down in 1965, some have talked about a possible rebirth of the project but using the same nuclear explosive propulsion as it was originally intended to use. However, I take it one huge refit further by changing the propulsion system to a safer and more efficient one which was pioneered by Project Daedalus.
In the late 1960s and early 1970s, researchers literally banned the bomb from nuclear pulse propulsion research and turned the pusher plate into a magnetic field for fusion micro explosions. In the 1970s the British Interplanetary Society revisited the Orion Concept and did a five-year theoretical study called Project Daedalus of n interstellar probe flyby mission to Barnard's Star. Daedalus pioneered deuterium-helium3 fusion pulse propulsion using laser-triggered inertial confinement fusion (ICF). A Daedalus probe would be 190m long and almost as wide as it is long as well as divided into two stages. Daedalus would carry 50,000 tonnes of D-He3 propellant and be 54,000 tonnes when fully fueled with only 4,000 tonnes of dry mass which would include a 450 tonne payload. The helium3 would be mined from the atmosphere of Jupiter for Daedalus. Daedalus would accelerate to 12%c for four years and would not decelerate to its destination and instead fly by it. In the payload bay there would be an astronomy deck with telescopes and an array of smaller probes that deploy from the main craft upon approach of the destination. It is from Daedalus that Orion borrows is new primary propulsion system, astronomy deck, and dispatch probes.
On September 30, 2009, the British Interplanetary Society and the Tau Zero Foundations started a joint study of an interstellar probe that would actually decelerate to the destination. And this current five-year-study is called Project Icarus. Daedalus is too massive so Icarus is designed to be less massive and to have a secondary propulsion system such as a solar sail or a magsail to save propellent and mass. Unlike Daedalus, Icarus would have its helium3 mined from Uranus. Icarus is designed with a fifteen-light-year radius in mind to encompass several target star systems including Alpha Centauri (4.37ly), Epsilon Eridani (10.5ly) and Tau Ceti (11.9ly). Icarus can travel from 10-20%c. Orion in its second life has considered a secondary propulsion system such as a magsail even before Icarus started.
I got totally hooked on Project Orion on Monday, August 17, 1998 and due to comprehension issues that I had at the time thought that it was not defunct until someone told me up front in the morning of Thursday, February 18, 1999. In response I revamped Orion by changing it to having a safer and ore efficient propulsion pioneered by Daedalus system and from that day on until recently used to call it "Orion II" or "Project Orion II". I now call my D-He3 Orion and extension of Project Orion.
Currently, Project Orion is planned by me to use a Daedalus/Icarus-style D-He3 fusion pulse propulsion system that might me antimatter-assisted and a secondary propulsion to save propellent and mass. Like Icarus, Orion will have a 15-light-year radius for interstellar missions. Orion will mine its helium3 from the moon, solar wind, and Uranus.