During the Cold War, the United States initiated Project ORION. This program was intended to build and launch super-heavy vehicles into space. They wanted to do this not with the use of chemical boosters, but rather by detonating small nuclear charges on the other side of a suspended plate which transfers momentum to the crewed vehicle. However due to bureaucratic conflict and fallout concerns, Project ORION never actually materialized.

What change would have to take place during this process for Orion-type spacecraft to become a reality? By this I mean a world where eventually multiple such vehicles are launched and they see regular use in space operations.

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    $\begingroup$ Aren't you answering your own question? due to bureaucratic conflict and fallout concerns, Project ORION never actually materialized $\endgroup$
    – L.Dutch
    Jul 27, 2020 at 19:33
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    $\begingroup$ I suggest reading Footfall by Niven and Pournelle. No spoilers, but there's an Orion vehicle in the novel... $\endgroup$
    – Zeiss Ikon
    Jul 27, 2020 at 19:34
  • $\begingroup$ @ZeissIkon To continue in the "no spoilers" vein: Let's say a certain measure of desperation would let people re-evaluate merits and risks of such a vehicle ;-). $\endgroup$ Jul 28, 2020 at 7:34
  • $\begingroup$ From up wind and as many, many miles away. $\endgroup$
    – Mon
    Jul 28, 2020 at 12:15
  • $\begingroup$ The Partial Test Ban Treaty of 1963 banned atmospheric detonations of atomic bombs and killed off Project Orion. I suppose you could assemble the craft in space, but the Outer Space Treaty would prohibit nukes in space. en.wikisource.org/wiki/Partial_Test_Ban_Treaty $\endgroup$
    – Tangurena
    Jul 28, 2020 at 22:22

5 Answers 5


Project Orion never came to fruition for multiple reasons, chiefly among them that there was no purpose for it.

Remember, the space race, Moon landing, etc. didn't happen because people were totally pumped about space exploration or because scientists wanted to fulfill their curiosity, or even because people wanted to colonize other worlds; it all happened because the USA wanted to beat Russia. It was a matter of national pride, prestige, and asserting dominance over communism, not building cool spaceships.

If there had been a good reason to develop Nuclear Pulse Propulsion into a viable vehicle, it would've happened (and could still happen). The technology and theory behind it is sound, and while difficult, the engineering hurdles are manageable with today's (and even Apollo-era) technology.

But, it looks like you're asking for speculation, so let's speculate:

Some historical reasons that might've caused project Orion to proceed

  • The USA is losing the cold war, the Soviets won the race to the moon, and the USA somehow concludes that they need to do something wild like colonize the Moon, Mars, or Jupiter
  • Project Orion somehow became the passion project of multiple high-level people including the president and enough legislators and military people to make it work

Some modern/timeless reasons why someone might build a NPP spacecraft

  • Literal hostile aliens show up and the world needs spacecraft that can attempt to match alien capabilities. At this point, nuclear accidents are OK because it's deemed the planet is screwed if the aliens win anyways
  • There is enough money available for a serious, well-funded effort to explore other solar systems
  • Countries have space military with battleships and space marines. They need a powerful ship design and NPP is deemed the best option
  • Enough in-solar-system travel exists along with abundance of nuclear material to make it financially viable for companies to use NPP ships

A multitude of actual answers were developed during the period when ORION nuclear pulse drive were being actively investigated, but references are scattered all over the place, making it difficult to encapsulate this. Some of the best sources of information are through the Atomic Rockets website and the "Unwanted Blog", who's author is a big fan. A man named Anthony Zuppero also came up with an.....interesting......use for ORION, which will also be discussed.

While 4000 ton space battleships were seriously being proposed (having Minuteman ICBM's as their main battery, 5" naval gun turrets for close defence and so on, this was really more than a bridge too far. Much smaller ORIONs were pitched to NASA and the USAF, with the size constraint being the diameter of the drive plate had to fit a Saturn V booster for lift off.

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Model of the 4000 ton space battleship proposal. Yes, this was actually a real proposal

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USAF/NASA "10 metre" ORION. This was to be boosted by a Saturn V into orbit. From the Unwanted Blog

By 1965, the ORION program was winding down, but General Atomics tried to sell the USAF on the program with a scaled down set of spacecraft, such as an emergency command and control center (blasted into orbit from a ground silo), an orbiting command post and a "bomber" on a long looping orbit which took it past the Moon and made it extremely difficult to intercept or eliminate America's nuclear deterrent. These were meant to be lofted by clusters of solid fuel boosters ranging from 7 120" solid fuel boosters (derived from the Titan III boosters) to 156" solid fuel boosters (4 for a lightweight ship and 7 for a heavy ship...)

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Emergency command post lifting off

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Model of proposed USAF ORION command post spacecraft

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Bomber ORION on it's launch stack

So ORION could be launched by various means. The launching of ORION using rockets actually invalidated much of the reason for having ORION in the first place: being able to launch heavyweight spacecraft from Earth. The idea of radioactive fallout and EMP from launch made launching ORION using nuclear pulse units a political non starter. However, if it is the end of the world, then perhaps that is no longer a consideration.

Anthony Zuppero wrote an interesting memoire about his time working in the defence industry. as a thought experiment, he was asked to find a way to disable Soviet nuclear missiles in their launch fields "in two minutes" in order to prevent them from being launched. Zuppero went on to design perhaps the largest semi plausible weapon ever - a 5 gigaton weapon launched from the United States on an ORION pulse drive...The thought of the largest nuclear weapon ever conceived riding skyward on a pillar of nuclear fire is, well...

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Schematic of the Doomsday ORION by [William Black]. The design for the actual 5 Gigaton warhead is strictly conjectural.11

So in terms of making ORION a plausible vehicle, there is no doubt that it was, and using 1960 era technology as well. The idea of a high thrust, high ISP drive is still viable, but would have to be only for very extreme conditions, such as saving the world:


An unmanned Orion asteroid interceptor was designed. It would not need shock absorbers. Artillery arming, fusing, firing system for shells are regularly built to take 1000 Gs.

There was a three page paper: Nuclear explosive propelled Interceptor for deflecting objects on collision course with Earth. Johndale Solem, Los Alamos, proposed unmanned vehicle. No shock absorber or shielding. The pulse units were 25kg bombs of 2.5 kiloton yield.

Get to high velocities with only a few explosives and small shock absorbers or no shocks at all. Launch against a 100 meter chondritic asteroid coming at 25 km/sec. 1000 megatons if it hits. Launch when it is 15 million kilometres away and try to cause 10000km deflection. A minimal Orion weighing 3.3 tons with no warhead would do the job. 115 charges with a total of 288 kiloton yield. Launch to intercept in 5 hours. Ample time to launch a second if the first failed.

Outside of asteroid destroying interceptors, the ability to use ORION to launch heavy payloads from the ground is pretty much a dead letter. However, since ORION nuclear pulse drive is the only plausible high thrust, high ISP drive currently known (fusion drives need to actually demonstrate fusion before they can be considered), it will be highly desirable for deep space missions. In order to get the maximum performance from ORION, and use the smallest possible pulse units (people will be nervous about nuclear detonations in space, despite the fact space is already a high radiation environment, and particles from a nuclear explosion are moving at far beyond escape velocity, so will never return to Earth), the ORION formula will have to be inverted.

MEDUSA is a proposal to "invert" the ORION, with the plasma from the pulse projected against a gigantic "sail" ahead of the spacecraft. The thrust was transmitted to the spacecraft via a huge network of cables, making the entire structure in tension, and thus far lighter than the equivalent pusher plate structure. Since the sail is far larger than any conceivable pusher plate, much more of the energy can be captured. Combining this with a much lighter overall spacecraft system makes MEDUSA a wonderful method of transporting large payloads to the outer Solar System in a fraction of the time compared to other proposed methods. enter image description here

Schematic of MEDUSA in operation

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MEDUSA nearing Saturn

So the best way to make ORION a feasible and workable system for actual use is to have it as a deep space propulsion system, capable of moving large payloads to the outer Solar System in reasonable amounts of time compared to ion, nuclear thermal or other known systems. This in turn requires some plausible and economically feasible reason to actually go to the outer Solar System. A few plausible reasons may exist:

  1. Anti protons are captured by the magnetospheres of planets. The giant planets, with their huge magnetospheres, will capture usable amounts (micrograms, but antimatter is extremely potent), making rapid deep space travel economically viable. Capturing antimatter and sending it to Earth as an extremely compact energy storage and generation method is a plausible reason to do deep space missions.

  2. Titan's atmosphere contains millions of tons of hydrocarbons. These are useful as chemical feedstocks for plastics, pharmaceuticals and fertilizers, among other things. A space economy will need these products, and having a "local" source that does not need to be lifted from a deep gravity well is a bonus.

  3. Titan's atmosphere and extreme cold conditions also make it potentially the industrial powerhouse of the Solar System. The Carnot equation tells us efficiency is measured by the differential between the hot and cold side of a system. On Earth, the "cold" side is at atmospheric temperatures, but on Titan, the atmospheric temperature is hundreds of degrees below 0 C, meaning most processes and computing become far more efficient compared to the same things on Earth. This makes cheap, high speed transport vital.

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Carnot Efficiency. When the difference between tH and tL are larger, the efficiency goes up

So with sufficient reason to actually go to deep space destinations, ORION and its variants will be highly desirable due to their high thrust and high ISP, making fast and cheap transportation possible.

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    $\begingroup$ The MEDUSA program looks like an incredibly bad idea, as you're pulling your payload right through the remains of your nuclear explosion, which is not great for either living organisms or computer equipment. You could beef up the radiation shielding to protect it, but that possibly negates the benefits of this method by adding weight. Maybe a variation with two or more sails off to the sides of the ship's trajectory path might be a safer alternative? $\endgroup$ Jul 28, 2020 at 14:03
  • $\begingroup$ @DarrelHoffman: along the idea of rubber slingshot on a Y-shaped stick? won't work, because noone is holding the stick and 'vertical' aiming is hard (noone is holding the munition and aiming up/down with it while applying tension to the rubber). However, if we arrange it all into a triangle, sails at the corners, equal&synchronized charges/etc, then the payload can be flung through the center of the triangle, far from corners. We could do a square/hexagon/etc as well - it just makes synchronization a bit harder, but charges would be smaller. 100-point launch array would resemble a warp gate :D $\endgroup$ Jul 28, 2020 at 14:47
  • $\begingroup$ @quetzalcoatl I think of it more like a team of horses or sled dogs or something, only instead of all the "horses" being in rows directly in front of the carriage, they're off to the sides (sides in this case being every direction since you're in space), still connected to it by cables though, not so much like a slingshot which is separate from the projectile. A circle of sails all tethered to the payload might be better, though as you say the synchronization is trickier. $\endgroup$ Jul 28, 2020 at 18:00
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    $\begingroup$ The pictures don't give a real idea of the scale, and since space is radioactive anyway. your ship will be well shielded from the nuclear pulse. Orion nuclear pulse units direct 85% of the energy into the pusher plate or spinnaker anyway, away from the payload. $\endgroup$
    – Thucydides
    Jul 29, 2020 at 2:14

The Earth is dying:

One possible scenario is that some vast catastrophe has or will soon devastate the future capacity of the Earth to sustain human life. In such a situation, getting MASSIVE amounts of stuff into space as quickly as possible, regardless of the consequences, would become the overarching concern.

Say, for example, an asteroid was headed to Earth and scientists couldn't figure out how to stop it. Or a bunch of asteroids. Like ten dino-killers at once. Maybe they still try to divert it/them, but just in case, we want to built a gigantic space station. Also just in case, we build a fleet of Orion colony ships to get survivors off the Earth in case attempts to stop the asteroids fail.

To jump-start this, the (US government? Russians? Chinese?) have been investing in the tech just in case the world was going to come to an end. They share the engineering, because they can't build them fast enough on their own, and fear that if they are the only survivors, vengeful rivals will kill (literally) the project.

Even with Earth devastated, it would still be a huge, nearby source of material for our space colonists, and they would need a big spacecraft to haul tons of (dirt/water/metals) back into space.

Once people accepted the Orion design, even if the asteroids were diverted (or especially if the Orions were central to diverting the asteroids) the ships would be accepted as established tech.


Launch from international waters.

The main obstacle to launching Orion Drive spacecraft is a political one, the result of nations deciding against the use of nuclear explosions for peaceful purposes lest they accidentally start a nuclear war, and writing treaties with other banning their use.

As a result, if you wanted to launch Orion Drive nuclear pulse rockets, you would need to find a way to circumvent those treaties. Fortunately, there’s already a way to do so: international waters.

The idea is fairly simple: you buy an oil rig, park it out in international waters, have it fly a flag of convenience of a nation that hasn’t signed those treaties, and convert it into a manufacturing facility for the nuclear pulse fuel units. You also build your Orion Drive nuclear pulse rockets as seaplanes (again, flying a flag of convenience), and have them take off conventionally from the ocean surface, and then start the nuclear pulses once airborne.

The result would be a rocket that is somewhat less efficient than a more conventional, land-based rocket, since it would have to carry the mass of its wings and reinforced seaplane body into orbit with it, but it would be theoretically legal to build and operate.

  • $\begingroup$ Why not ditch the wings like any other staged rocket as soon as you don't need them? Or just launch directly from the water, like Sea Dragon was supposed to? $\endgroup$ Jul 28, 2020 at 1:23
  • $\begingroup$ @LoganR.Kearsley I don't think an underwater nuke would go well $\endgroup$
    – DKNguyen
    Jul 28, 2020 at 1:39
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    $\begingroup$ @DKNguyen Why not? The thrust ought to enhanced with the denser medium to contain the explosion. And if for some reason it is a problem, you can just gain initial altitude with conventional explosives, which is the land-launch procedure anyway. $\endgroup$ Jul 28, 2020 at 3:45
  • $\begingroup$ @LoganR.Kearsley Because that'd increase the cost of each flight, compared to a fully-reusable rocket - and when you've got the thrust to launch thousands of tons of mass to the moon and back on one tank of fuel, you might as well make the rocket fully reusable. The wings would also allow you to more easily glide in for a landing, as well. $\endgroup$
    – nick012000
    Jul 28, 2020 at 4:03
  • $\begingroup$ @nick012000 That depends on how much extra fuel you need to carry the wings. Bomb-grade fission fuel isn't exactly cheap. And you could always make the wings independently recoverable and reusable. $\endgroup$ Jul 28, 2020 at 5:08

A 2012 study in the Journal of Propulsion and Power directly addresses your question: "[Project Orion's] feasibility was never dismissed on purely technical grounds. In fact, many of the scientists and engineers who came into contact with the program over its seven-year lifetime became convinced of its viability. The political and nontechnical issues that finally sealed the program's fate would certainly make the original Orion unacceptable by today's standards. However, new technologies and ideas developed since then could mitigate some of the major issues, and make nuclear pulse propulsion less unreasonable to consider for future human exploration." According to the authors, there's nothing technical keeping the ORION program from being restarted. If you want more details, here's another proposal. And if you want a lot more detail, here's an entire book on different forms of nuclear propulsion.


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