Project Orion

Monday, December 5th, 2011

Project Orion seems like the kind of project Nazi rocket-scientists would have dreamed up — a rocket propelled by intermittent nuclear bomb explosions — but the general proposal came from Stanislaw Ulam, a Polish Jew who had come to the States before his homeland was invaded, and the preliminary calculations were made by Frederick Reines, the son of Russian Jews who had come to the States a generation earlier:

During the war, Ulam and Frederick Reines considered nuclear propulsion of aircraft and rockets. This is an attractive possibility, because the nuclear energy per unit mass of fuel is a million times greater than that available from chemicals. From 1955 to 1972, some of their ideas were pursued during Project Rover, which explored the use of nuclear reactors to power rockets.
In 1955, Ulam and C. J. Everett proposed, in contrast to Rover’s continuous heating of rocket exhaust, to harness small nuclear explosions for propulsion. Project Orion was a study of this idea. It began in 1958 and ended in 1965, after the Partial Nuclear Test Ban Treaty of 1963 banned nuclear weapons tests in the atmosphere and in space. Work on this project was spearheaded by physicist Freeman Dyson, who commented on the decision to end Orion in a famous article, “Death of a Project“.

Orion offered high thrust and high specific impulse, or propellant efficiency, at the same time. Traditional chemical rockets produce high thrust, but produce it inefficiently, and electric ion engines efficiently produce small thrust.

The key to the design is the elimination of any kind of combustion chamber:

Instead, bombs would be ejected backwards from the vehicle, followed by solid-propellant disks. The explosions would vaporize the disks, and the resulting plasma would impinge upon a pusher plate. The advantage of this system is that no attempt is made to confine the explosions, implying that relatively high-yield (hence high-power) bombs may be used. Such a system is neither temperature- nor power-limited. Ulam may have been influenced by experiments conducted at the Eniwetok proving grounds, where graphite-covered steel spheres were suspended thirty feet from the center of an atomic explosion. The spheres were later found intact; a thin layer of graphite had been ablated from their surfaces.

Although the project was not full of Nazi rocket-scientists, it did follow certain German models:

Project Orion was born in 1958 at General Atomics in San Diego. The company, now a subsidiary of defense giant General Dynamics, was founded by Frederick de Hoffman to develop commercial nuclear reactors. The driving force behind Orion was Theodore Taylor, a veteran of the Los Alamos weapons programs. De Hoffman persuaded Freeman Dyson, a theoretical physicist then at the Institute for Advanced Study in Princeton, New Jersey, to come to San Diego to work on Orion during the 1958-1959 academic year. Dyson says that Taylor adopted a specific management model for the project: the Verein fur Raumschiffahrt (VfR), the German rocket society of the 1920′s and 1930′s which numbered among its members Werner von Braun. The VfR had little structure: no bureaucracy and essentially no division of labor between its members; it accomplished much before it was taken over by the German army. Orion at first was similar: scientists did practical engineering and engineers built working scale models, all on a shoestring budget.

If your team is planning on setting off repeated atomic bomb blasts behind a rocket and smoothing those blasts out with an enormous pusher plate hooked up to shock absorbers, it’s the kind of team that thinks BIG:

At a time when the U.S. was struggling to put a single man into orbit aboard a modified military rocket, Taylor and Dyson were developing plans for a manned voyage of exploration through much of the solar system. The original Orion design called for 2000 pulse units, far more than enough to attain Earth escape velocity. “Our motto was ‘Mars by 1965, Saturn by 1970′”, recalls Dyson. Orion would have been more akin to the rocket ships of science fiction than to the cramped capsules of Gagarin and Glenn. One hundred and fifty people could have lived aboard in relative comfort; the useful payload would have been measured in thousands of tons. Orion would have been built like a battleship, with no need for the excruciating weight-saving measures adopted by chemically-propelled spacecraft.

Chemical rockets, the Orion team felt, weren’t good for going much past the moon — but that wasn’t an issue for the folks handing out defense dollars. They only needed a rocket that could reach the next continent.

And NASA didn’t want to be tarred with the nuclear brush.

Maybe the Chinese’ll give it a go…


  1. Borepatch says:

    What happens when it wants to leave Earth orbit, and the bombs cause repeated Electromagnetic Pulse events?

  2. Cygnus Darkstar says:

    That isn’t a problem, as the Compton scattering that produces EMP can only occur inside an atmosphere. The effects of EMP are ridiculously overblown in the popular conception anyway; conditions have to be just right for it to be dangerous.

  3. Ham Sandwich says:

    I wonder what use Orion would really be. It is really the only hope for interstellar travel, but it would take so long to get there and back that any interstellar trip would leave the closed loop of human life in our solar system and effectively never return.

    And for trips around the solar system (at least to and from anyplace potentially useful) wouldn’t NERVA engines work well enough and be much cheaper to operate?

  4. Isegoria says:

    When Project Orion was still being considered, in the 1940s and ’50s, EMP was understood to be a local phenomenon. It was 1962′s Starfish Prime test, at high altitude, that caused a much larger EMP than expected, through what is now called the Compton Effect.

    Anyway, fallout was the chief concern at the time, but EMP is a recognized problem:

    The launch of such an Orion nuclear bomb rocket from the ground or from low Earth orbit would generate an electromagnetic pulse that could cause significant damage to computers and satellites, as well as flooding the van Allen belts with high-energy radiation. This problem might be solved by launching from very remote areas, because the EMP footprint would be only a few hundred miles wide. The Earth is well shielded by the Van Allen belts. In addition, a few relatively small space-based electrodynamic tethers could be deployed to quickly eject the energetic particles from the capture angles of the Van Allen belts.

  5. Isegoria says:

    The chief advantage of Orion is that you can launch a massive vehicle into space and really rocket around the solar system, like a sci-fi rocket ship, not a floating tin can.

    NERVA engines are efficient but offer low thrust.

  6. Buckethead says:

    Isegoria, NERVA rockets aren’t typically classed as low thrust — they can achieve thrust in the same ballpark as a chemical rocket. They are more efficient than chemical rockets at maybe 1000 Isp, but no where near the 10,000 Isp of even a minimal Orion design, or the 20,000 Isp (potentially) of a VASIMR thruster. The VASIMR, like all plasma thrusters, has very low thrust.

    Of all the types of propulsion we could use right now, without waiting for physics breakthroughs, Orion is unique in offering much higher thrust and much higher efficiency. And it is more efficient the bigger you make it up to millions of tons of payload.

    Maybe others can’t see a reason for an 8 million ton reference Orion design capable of taking hundreds of people to Saturn in a couple months. But I think that really is a failure of imagination on their part.

  7. Isegoria says:

    Nuclear thermal rockets appear to have twice the specific impulse of chemical rockets and one-tenth the thrust-to-weight ratio:

    Using hydrogen propellant, a solid-core design typically delivers specific impulses (Isp) on the order of 850 to 1000 seconds, about twice that of liquid hydrogen-oxygen designs such as the Space Shuttle Main Engine.
    Immediately after World War II, the weight of a complete nuclear reactor was so great that it was feared that solid-core engines would be hard-pressed to achieve a thrust-to-weight ratio of 1:1, which would be needed to overcome the gravity of the Earth on launch. The problem was quickly overcome, however, and over the next twenty-five years U.S. nuclear thermal rocket designs eventually reached thrust-to-weight ratios of approximately 7:1. Still, the lower thrust-to-weight ratio of nuclear thermal rockets versus chemical rockets (which have thrust-to-weight ratios of 70:1) and the large tanks necessary for liquid hydrogen storage mean that solid-core engines are best used in upper stages where vehicle velocity is already near orbital, in space “tugs” used to take payloads between gravity wells, or in launches from a lower gravity planet, moon or minor planet where the required thrust is lower. To be a useful Earth launch engine, the system would have to be either much lighter, or provide even higher specific impulse. The true strength of nuclear rockets currently lies in solar system exploration, outside Earth’s gravity well.

  8. Buckethead says:

    Sure. But the fact that you can talk about getting a thrust-to-weight ratio of at least one puts you in the “high thrust” area. You could never use a Hall effect thruster to take off from Earth.

    Some proposed designs for pebble-bed reactors could conceivably better the thrust-to-weight ratio considerably, removing as they do the need for heavy reinforcing structure for the reactor core.

  9. Makes you wonder what the minimum personal cache is for space propulsion systems.

  10. Buckethead says:

    Well, for me it would be an 8 million-ton Orion. I’d go and set up a fortress of solitude on Saturn’s moon Mimas, since it looks like the death star anyway.

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