From The Editor | September 6, 2023

Nuclear Dreams: The Race To Build Project Orion

John Oncea

By John Oncea, Editor


Project Orion was a conceptual design for a spacecraft propulsion system that was developed during the late 1950s and early 1960s. Ambitious and innovative, the project's goal was to develop a spacecraft capable of carrying humans to distant destinations – including Mars and beyond – using nuclear explosions for propulsion.

I just began listening to Everything Everywhere Daily, a history, society, and culture podcast published by Gary Arndt and Glassbox Media. It’s very good and I can’t recommend it enough.

If you’re going to give it a listen – and I know you are – start with Project Orion, the story about several Manhattan Project scientists who, immediately following the end of World War II, “Wondered if we could harness the incredible power of atomic bombs and put them to use for peaceful purposes. In particular, what if we could use atomic bombs to literally blast ships into space?”

Again, go ahead and give it a listen, and also check out this TED Talk by author and historian George Dyson, son of theoretical physicist Freeman Dyson who worked on Project Orion from 1957 to 1961. In the TED Talk, the younger Dyson shares an “insider’s perspective and a secret cache of documents (that) bring an Atomic Age dream to life.”

But, before you do, finish up this article.

First, A Brief History Of Nuclear Propulsion

Nuclear propulsion uses nuclear reactions to produce energy for vehicle propulsion. There are three main types: naval, aero-nuclear, and space, according to the book Propulsion Systems - Recent Advances, New Perspectives and Applications.

The book’s authors, Bahram Nassersharif and Dale Thomas, write that naval nuclear propulsion offers numerous advantages over traditional propulsion techniques, such as improved range, speed, and maneuverability. The USS Nautilus, commissioned in 1955, was the first nuclear-powered submarine and today many submarines and aircraft carriers rely on uranium-fueled nuclear reactors for long-lasting propulsion without the need for frequent refueling. The U.S. Navy alone has 11 aircraft carriers and nearly 70 submarines in service, all powered by nuclear reactors.

Aero-nuclear propulsion uses nuclear reactors to power aircraft or missiles and has undergone extensive research and development over the years. Finally, space nuclear propulsion, which involves the use of nuclear reactors to power spacecraft and provides increased speed and efficiency compared to traditional propulsion methods.

Discussions about using nuclear material to power cars, planes, and boats began at the start of the 20th century with radium initially considered as a potential fuel source. However, it wasn’t until the “mid-twentieth century when the development of the atomic bomb and the dawn of the nuclear age sparked a new era of technological innovation and exploration,” write Nassersharif and Thomas. “As the world rapidly discovered nuclear technology’s tremendous power and potential, scientists and engineers began exploring new ways to harness this power for practical applications.”

This concept comes with several advantages over chemical propulsion systems including:

  • High-Specific Impulse: Nuclear propulsion systems can provide significantly higher specific impulse (a measure of propulsion efficiency) compared to chemical rockets. This means they can achieve higher speeds and carry larger payloads.
  • Long-Duration Missions: Nuclear propulsion is well-suited for missions that require extended operation in space, such as crewed missions to Mars or deep space exploration.
  • Reduced Travel Time: Faster propulsion can reduce the time it takes to reach distant destinations within the solar system.

“Despite its many benefits, nuclear propulsion also posed significant challenges and risks, including the need for safe and reliable power sources, effective shielding to protect against radiation exposure, and rigorous regulatory and licensing processes,” Nassersharif and Thomas write. “These challenges led to the development of new technologies and processes for designing and operating nuclear propulsion systems. By the end of the twentieth century, nuclear propulsion had become a critical component of many military and space programs.”

One of the most interesting and storied nuclear propulsion projects, Project Orion, was proposed in the late 1950s and early 1960s and involved using nuclear explosions to propel a spacecraft.

A Gateway To The Stars

Project Orion was developed by scientists in the late 1950s and early 1960s, primarily by physicist Freeman Dyson and a group of scientists known as the “Orion Team” under the auspices of the U.S. government's Advanced Research Projects Agency (ARPA). The concept was conceived by Stanislaw M. Ulam and involved using atomic bombs to generate enough thrust to lift a ship into space.

It “was pretty simple, at least conceptually,” writes Interesting Engineering. “Bombs could be ejected backward from the vehicle, followed by solid-propellant disks. The explosions would vaporize the disks, and the resulting plasma would impinge upon a pusher plate.

“Using this nuclear pulse propulsion, the design for the ship envisioned a large plate, a ‘pusher,’ beneath which an atomic bomb would detonate. The energy released by this explosion would drive the pusher away from the blast at a speed fast enough to achieve escape velocity.”

To achieve space travel, it would require a series of atomic explosions to propel a ship into orbit. One bomb would not be enough, and approximately 800 bombs the size of a small compact car would need to explode beneath the ship at a rate of one per second. This was necessary for Orion and Super Orion-class ships to remain in orbit and prevent them from falling back to Earth.

This unconventional propulsion method was theoretically capable of achieving much higher speeds than traditional chemical rockets resulting in faster interplanetary and interstellar travel. However, concerns over nuclear fallout and environmental impact led to the project’s cancellation in 1964 after seven years of work.

“The design effort was carried out at General Atomics in the late 1950s and early 1960s,” writes the American Nuclear Society (ANS). “The idea of Orion was to react small directional nuclear explosives against a large steel pusher plate attached to the spacecraft with shock absorbers.

“Efficient directional explosives maximized the momentum transfer, leading to specific impulses in the range of 6,000 seconds, or about 12 times that of the Space Shuttle Main Engine. With refinements, a theoretical maximum of 100,000 seconds (1 MN·s/kg) might be possible. Thrusts were in the millions of tons, allowing spacecraft larger than eight million tons to be built with 1958 materials.”

A steel submarine-style construction was planned for the reference design, with a crew of over 200 and a vehicle takeoff weight of several thousand tons. This low-tech single-stage design would allow a round-trip to Mars from the Earth's surface in just four weeks, which is significantly shorter than NASA's current chemically powered reference mission that takes about 50 weeks. Additionally, the same craft could visit Saturn’s moons in just seven months, compared to the nine-year duration of chemically powered missions.

During the project, several engineering issues were discovered and resolved, particularly concerning crew shielding and pusher-plate lifespan. The system seemed entirely feasible and was undergoing significant development in the U.S. However, the project was terminated in 1965 due to the Partial Test Ban Treaty, which made it unlawful to conduct nuclear explosions in space. Before the treaty, both the U.S. and the Soviet Union had already detonated at least nine nuclear bombs, including thermonuclear bombs, at altitudes over 100 km.

“There were also ethical issues that would be associated with launching such a vehicle from within the earth's magnetosphere,” ANS writes. “Calculations showed that the fallout from a takeoff could be projected to lead to the premature death of between 1 and 10 people. Thus, this project would be entirely feasible if the ship were launched from outside the magnetosphere – the only remaining difficulty being, of course, transporting everything to the launch point.”

And Then, It Was Over … Or Was It?

Project Orion was canceled in 1965 due to funding problems and the signing of the Nuclear Test Ban Treaty in 1963. The treaty outlawed all nuclear tests in space, making it impossible to develop Project Orion and greatly reduced political support for the project. Other reasons included the Partial Test Ban Treaty which banned nuclear explosions in space, and various other test ban treaties and space weapons treaties which do not allow the exploding of nuclear weapons anywhere other than deep underground.

Project Orion was just the first engineering design study of atomic explosion propulsion. Six years after Project Orion was canceled Project Daedalus, a British interstellar spacecraft design that aimed to reach Barnard's Star, began. It was based on the concept of nuclear fusion propulsion, specifically using deuterium and helium-3 as fuel and while it was never built, it served as a significant study in advanced propulsion technology.

Other studies followed including Project Longshot, a U.S Naval Academy-NASA nuclear pulse propulsion design; AIMStar, a proposed Antimatter-catalyzed nuclear pulse propulsion craft that uses clouds of antiprotons to initiate fission and fusion within fuel pellets; ICAN-II, a proposed crewed interplanetary spacecraft that used the antimatter-catalyzed nuclear pulse propulsion engine as its main form of propulsion; and External Pulsed Plasma Propulsion (EPPP), a propulsion concept by NASA that derives its thrust from plasma waves generated from a series of small, supercritical fission/fusion pulses behind an object in space.

Flash forward to early 2023 and a NASA/DARPA announcement of a project aimed at using nuclear power to eventually transport astronauts to Mars. “NASA will work with our long-term partner, DARPA, to develop and demonstrate advanced nuclear thermal propulsion technology as soon as 2027,” said NASA Administrator Bill Nelson. “With the help of this new technology, astronauts could journey to and from deep space faster than ever – a major capability to prepare for crewed missions to Mars.”

NASA's Space Technology Mission Directorate (STMD) will be responsible for the technical development of a nuclear thermal engine that will be incorporated into an experimental spacecraft being developed by DARPA. DARPA will act as the contracting authority for the entire stage, including the reactor, and will lead the program's overall development, which includes rocket systems integration and procurement, approvals, scheduling, security, safety, and liability. DARPA also will ensure the overall assembly and integration of the engine with the spacecraft. Throughout the development process, NASA and DARPA will work together on the engine's assembly, with an in-space demonstration planned as early as 2027.

“With this collaboration, we will leverage our expertise gained from many previous space nuclear power and propulsion projects,” said Jim Reuter, associate administrator for STMD. “Recent aerospace materials and engineering advancements are enabling a new era for space nuclear technology, and this flight demonstration will be a major achievement toward establishing a space transportation capability for an Earth-Moon economy.”

At the time of the announcement, according to Spectrum News, there were questions about just how safe a nuclear-powered rocket would be. Recently, officials at the Demonstration for Rocket to Agile Cislunar Operations (DRACO) program want on record as saying the program is safe.

“The reactor will not explode,” DARPA program manager for DRACO, Tabitha Dodson, assured Spectrum News. “Additionally, as long as the reactor is not turned on, it will not generate any … fission products. If there is some kind of first-stage launch vehicle failure that breaks the reactor and exposes the core, the materials in the core will be safe to those around the launch site.”

“In a nuclear thermal rocket engine, a fission reactor is used to generate extremely high temperatures,” NASA added. “The engine transfers the heat produced by the reactor to a liquid propellant, which is expanded and exhausted through a nozzle to propel the spacecraft.”

While Project Orion never progressed beyond the conceptual and early design phases, it remains a fascinating chapter in the history of space exploration. Its audacious approach to propulsion demonstrated the creativity and ambition of scientists and engineers during the early days of the Space Age. Although the project was never realized, it contributed valuable lessons and ideas to the field of astronautics and propulsion technology.

For more information, check out George Dyson’s definitive history of the project, in which he details why a conventional chemical rocket the size of the Empire State Building would have been needed to accomplish what Project Orion might have been capable of.