Project Orion | Hacker News Reader

Project Orion

en.wikipedia.org

126 pointstosh69 comments

An other quite interesting concept (also a little less "out there" and actually, successfully tested) is the NERVA engine, also linked at the bottom of the article[1].

It uses a nuclear reactor to heat up a single propellant (liquid hydrogen) which then rapidly expands as it goes out the nozzle at the end, resulting in quite high specific impulse and is more efficient than a chemical rocket.

If we want to go really far out in terms of crazy rocket designs, there is also the concept of the nuclear salt-water rocket[2][3].

This one uses enriched plutonium or uranium salts, dissolved in water, inside a neutron-absorbent fuel tank design. The water is pushed out through a pipe, where an uncontrolled chain reaction starts. If it goes fast enough, it explodes right inside the engine bell, pushing the rocket. The proposed design in the original paper is supposed to generate hundreds of gigawatts of thermal power. This is comparable to the Chernobyl reactor #4 when it exploded, but unlike Chernobyl (which only exploded once) or the pulsed Orion engine, it could run continuously. The stuff that flies out of the nozzle easily reaches escape velocity of the solar system.

[1] https://en.wikipedia.org/wiki/NERVA?useskin=vector

[2] https://en.wikipedia.org/wiki/Nuclear_salt-water_rocket?uses...

[3] Obligatory Scott Manley video: https://www.youtube.com/watch?v=cvZjhWE-3zM

There's one more: the boring idea of combining a closed, electric-generating nuclear fission system with an (electric-powered) ion engine. Both components being flight tested and not crazy.

That doesn't sound like something that could get you off of the Earth.

It's probably a great choice for once you're already in space, where being able to apply even very small thrusts nearly-continuously really adds up.

The Soviets literally launched reactors into space in the late 70s for very high RF power radar satellites (intended to track US navy, among other things). One deorbited over northern Canada.

https://www.google.com/search?client=firefox-b-d&q=soviet+ro...

Of course anything related to hall effect/ion thrusters isn't going to get you off the earth even with some of the theoretical/bench-tested-only 100kW (electrical load) thrusters under development. These are things with very low thrust at any instantaneous moment in time but very high specific impulse from 3800 to 6000 ISP or more. Meant to be used in vacuum only.

Space based fission electric isn't very good though. Hence why they use PV now.

NASA are developing a system that aims to be 6.67We/kg https://en.wikipedia.org/wiki/Kilopower

Compare to 50We/kg for cheap consumer grade flexible PV designed to be kicked around for a decade including an inverter.

And that's with an atmosphere to use as a heatsink instead of radiators.

What is the specific power of a nuclear reactor + heat engine + crew shielding + radiators? Naval reactors are on the order of a few watts to tens of watts per kg and they have the benefit of unlimited cooling.

Seems an order of magnitude short of PV.

Possibly north of 200 W(elec.)/kg [0]. (I can't assess this stuff personally, but it's some MIT person's PhD thesis, so I assume some baseline credibility). Key distinction: you're looking at a conservative kilowatt-scale proposal, one which isn't intended for propulsion. But propulsion-optimized designs are on the megawatt scale: and the mass/power scaling is sub-linear.

[0] https://dspace.mit.edu/handle/1721.1/67559

Radiators scale at best linearly, so once they are dominant you don't get any improvement with power.

A mylar mirror is extremely cheap and light (kW or tens of kW of heat can be trivially concentrated per kg), so the fact that there are no even semi-serious proposals for space based CSP should be fairly telling as to the viabity.

At 200W/kg, a hypothetical fission generator is strictly worse than a current generation solar array in the inner planets for space based acceleration.

Seems useful outside mars though.

The nuclear salt reactor one is the answer to the question: "How can we make rocket engine testing more dangerous."

We don't have to build/test them on Earth.

I don't think it is "out there" really. It's pretty simple. Bombs, plate, boom. It went through a pretty thorough development cycle at General Atomics, and they didn't have modern simulators.

I think it would be great if we get a moon base going that could build it from regolith. Then you ship up the bombs in a few runs of Starship and you have a badass solar system exploration rig.

From the docs, they could get to Saturn in something crazy like 1 month.

And DoD and NASA are right now funding this research again.

Edit: NERVA style, not Salt water thing.

There was a classic science fiction story with a twist on this idea; a low tech species was about to be discovered by a more advanced species. And according to the rules of the more advanced species, any planet that wasn't capable of space travel would become a client or vassal, and a planet with space travel would be seen as a peer. The protagonist built a pusher style rocket using an explosive, and launched the lightest person he knew into orbit, who happened to be his girl friend.

I keep thinking this was a Larry Niven story, maybe someone here is familiar?

Edit; another classic story was the novel Footfall by Niven and Pournelle which featured launching the USS Missouri into orbit on an Orion style pusher to battle the invading aliens.

That doesn't sound part of Niven's Known Space canon.

However, 'Footfall' by Niven and Pournelle does have an Orion, as does Invisible Sun, by Charles Stross.

Nothing obvious in [0]

[0] https://en.wikipedia.org/wiki/List_of_stories_featuring_nucl...

It was a Niven / Pournelle mashup. Also, Lucifer's Hammer is a fun read I recall.

I very much have a soft spot for Footfall. Sending up a battleship kludged into an Orion style ship to battle alien invaders is just so cool.

I haven't read that book in 30 years, but the description of experiencing the launch from inside the craft was so succinct and evocative I still think about it from time to time.

"God was knocking and he wanted in bad."

One of my favourite lines ever! Note, it wasn't from the perspective of inside the craft but rather the towns people huddled in a bunker in Bellingham.

"King David's Spaceship". I believe it was by Niven, but I'm not sure.

"King David's Spaceship" aka "A Spaceship For The King" by Jerry Pournelle

It certainly is that book.

The wiki https://en.wikipedia.org/wiki/King_David%27s_Spaceship

It's been a long time since I read it... but the specifics of that part of the story:

> Back in Haven, Dougal's men used the acquired knowledge to build a primitive crewed spaceship, adopting a low-tech design of Robert Goddard—a rapid firing cannon using high-explosive shells detonating behind the ship to provide propulsion (but which might blow up the ship). Because the ship would not be airtight, only members of MacKinnie's company (who still had their space suits) could pilot it, and because it would only be able to carry a minimal payload, Graham (the lightest of the company) volunteered and was chosen as pilot. Before the launch, MacKinnie proposed to her, and she accepted. As soon as Prince Samual's World was unified, and in the presence of unsuspecting Imperial witnesses, Graham's ship was launched and achieved orbit, although it could not re-enter the atmosphere (meaning that the Imperials had to rescue Graham). King David then immediately requested that Prince Samual's World be admitted to the Second Empire as a self-governing world capable of crewed space travel, not as a colony.

> Footfall by Niven and Pournelle which featured launching the USS Missouri into orbit on an Orion style pusher

Yes, there was an Orion. No they didn't launch the USS Missouri. The ship was called Michael and featured, among other crazy weaponry, X-Ray lasers of the SDI type, i.e. some material (ruby?) pumped by a nuke. The nuke would destroy the material, but in the process get it to lase X-Rays. Heck, if you're using nukes for propulsion, might as well do that as well.

Maybe they repurposed the guns for something?

I distinctly remember some dialogue that there was some fairly rough welding of thick steel plates going on, none of the ultra-fine tolerances of traditional rocket engineering.

An orion spacecraft's best efficiency is a ship the size of millions of tons.

Yeah, you don't need to cross the T's on that as much.

replying to all... The story you're thinking of is King Davids Spaceship by Jerry Pournelle. It IS a co-dominion story (so same universe as The Mote in Gods Eye w/Larry Niven)

A few other uses of Orion in fiction that I am aware of:

The Ship 'Michael' (as in avenging angel) from Footfall (Again by Niven and Pournelle).

And the ship from Orion shall rise by Paul Anderson.

A CBC Miniseries featuring a (faked) Orion derived interstellar ark supposedly launched in the 60's and the people that have been living on it for almost 40 years.

> A CBC Miniseries featuring a (faked) Orion derived interstellar ark supposedly launched in the 60's and the people that have been living on it for almost 40 years.

I think it was from SyFy. It was so bad it could only be SyFy.

Could be a good murder mystery, if it were not ruined by the whole fake ship idea.

Yes, it was on SyFy, but was a CAD co-production so aired on CBC here.

This one I believe:

https://en.m.wikipedia.org/wiki/Ascension_(miniseries)

You have to rate a show like this relatively if you are watching on a network filled with crap. It was not bad for a SyFy show!

> Could be a good murder mystery, if it were not ruined by the whole fake ship idea.

Not quite what you are thinking, but you may enjoy Aniara:

https://m.imdb.com/title/tt7589524/

Speaking of sci-fi, project orion/nuclear propulsion is also featured in Marko Kloos' Frontlines series (though not in the first book if I remember correctly)

https://www.markokloos.com/?page_id=1859

The last book of the Remembrance of Earth's Past series (Death's End), also features a similar concept. They just send a brain into space though and use sails to capture the energy of the nuclear blasts.

There is a Kerbal Space Program mod [1] that adds this to the game. It is hysterically fun to use because it is insanely unbalanced compared to normal space flight requirements. Want to change your orbit 180deg and fly backwards? No problem. Goto any planet the "direct" route? Sure, why not. Take off from the launch pad so fast you'll think the game broke? Not a problem - The Kerbal's don't worry about a little fallout.

No idea how this would ever actually work in reality for manned spaceflight. For unmanned it seems relatively doable (ignoring the entire cost of getting it off the ground and into space first). But for a manned mission? Being subject to 2-4g is one thing, but to have it happen regularly... like a jackhammer almost? Sounds like a really bad trip. You could not do anything while that engine was firing (not that it'd be easy to do something under 2g constant acceleration) without risk of being in the wrong place/position at the wrong time. I don't know what the long terms effects of repeated, assumingly rapid, 2-4g pulsing is on the human body.... but I'd guess it falls under "can't be anything good" category.

[1] https://umbraspaceindustries.github.io/UmbraSpaceIndustries/

Based on the amount of time a Kerbal can survive orbiting the sun in their barely-shielded capsules, I am inclined to think that they are immune to radiation damage, like tardigrades.

Project Orion uses a pusher plate mounted on giant springs to spread out the force of each explosion. If the system is designed correctly it should result in constant acceleration.

So there are ways to make this interesting in the game and bring it back to balance. Some recommendations:

- The USI pulse nukes are expensive. Play on career mode so you are cash constrained and have to rigorously plan for their build, use, and refueling.

- Roleplay not using them anywhere near low home-planet orbit for fallout reasons. I.e. the ship is built and is parked in a shipyard in Cislunar space and kerbonauts must ride an intermediary shuttle vessel to crew it.

- Use a life support pack and planet mods that add interplanetary destinations. Having your kerbonauts on a nuke ship around an extrasolar planetary body far away from home with limited supplies will add plenty to the mix.

This was supposed to be in Kerbal Space Program 2, and you can see an early version of it in some of the promotional materials. Time will tell when it makes its way into the game.

Interstellar nuclear-powered transport (1968) [pdf] - https://news.ycombinator.com/item?id=28132756 - Aug 2021 (34 comments) - thanks antondd!

Orion Project [pdf] - https://news.ycombinator.com/item?id=22691219 - March 2020 (1 comment)

Nuclear Pulse Propulsion – Orion and Beyond (2000) [pdf] - https://news.ycombinator.com/item?id=12705705 - Oct 2016 (99 comments)

Project Orion (nuclear propulsion) - https://news.ycombinator.com/item?id=9025611 - Feb 2015 (11 comments)

Project Orion (nuclear propulsion) - https://news.ycombinator.com/item?id=3019627 - Sept 2011 (1 comment)

Project Orion is one of the stupidest, most wonderful ideas ever conceived in America. - https://news.ycombinator.com/item?id=261348 - July 2008 (6 comments)

That's less than I expected - are there other threads?

Interstellar nuclear-powered transport (1968) - https://news.ycombinator.com/item?id=28132756 - Aug 2021 (34 comments)

There are a few more, under different titles. I remember reading Dyson’s autobiography a couple of years ago and he mentioned his involvement in the research. Absolutely amazing stuff.

There’s a great BBC documentary on this called “To Mars by a Bomb”, highly recommend it. Was one of my first introductions to Freeman Dyson, ended up reading his autobiography as well. Was a remarkable man, and one of my favorite people to listen to.

It's on YouTube, and I second this recommendation.

https://youtu.be/xYoLcJuBtOw

I watched all 157 of these: https://www.youtube.com/playlist?list=PLVV0r6CmEsFzDA6mtmKQE... Really interesting.

I spoke to him once at a book signing and asked him about Orion. In summary he said: would it have worked - probably, should it be done - probably not. Although he did make the point that pretty much every big engineering project kills people.

Also some good physicist gossip. Apparently Teller was a big sulk and Oppenheimer was a massive pain in the arse (some of the time, anyway).

Added. Thanks!

Title should better be "Project Orion (nuclear propulsion)".

There's too many "Orion" things out there to make it clear that this specific one is about nuclear propulsion.

Thermonuclear Orion could (on paper) reach 10% the speed of light. Proxima Centauri in about 50 years using technology contemporary with the Beatles and Woodstock.

This is why I have trouble dismissing the Fermi paradox. Either intelligent life that can engage in space flight is very rare (as in less than one per galaxy per billion years) or we are in a wildlife preserve or a zoo.

Project Daedalus could reach 10% speed of light. But that didn’t use thermonuclear bombs but laser-pumped inertial confinement fusion. It also didn’t use physical pusher but magnetic nozzle. We don’t know how to do them with our technology but should be possible. There are followons that are more doable but slower.

I have seen Wikipedia quote 10% for regular Orion but not finding any sources. I find that speed unlikely with all the trouble that Daedalus and others went through to get interstellar pulse rockets. I see 6ksec impulse for could-build-now Orion, 100ksec for theoretical improvements, and Daedalus would be 1Msec. Regular Orion probably maxes out at 1%.

Fission Orion is infeasible for interstellar because need huge quantities of fissionables, maybe 10-100x weight of ship. Fusion has advantage of using cheap elements.

Makes me wonder if there ever will be a type of propulsion that doesn’t rely on throwing out mass behind a spaceship.

https://en.wikipedia.org/wiki/Solar_sail doesn't throw mass out the back. Although, it's not a lot of propulsion, it's something.

It still uses reaction mass; it’s just that it’s resupplied continuously by the Sun.

In some orbits around Earth and other planets with a string magnetic field, you can drive a ship by pushing on the planet. Also pretty low propulsion.

You can make it a couple times better by doing a close approach to the Sun. Within Mercury's orbit, you'll get 16 times (apologies for my napkin-quality math) the push it'd get around here.

And, with some mirrors, you can make a solar-thermal rocket as well.

All that makes me think: if today we decided to launch a Voyager-mass probe, what would be the maximum speed we could achieve with technologies we could deploy in a couple years (ruling out NTRs, liquid reactors, nuclear lightbulb or anything that requires a non-RTG fission reactor on board).

Imagining a chemical rocket for the initial push, then solar sail (maybe solar-thermal-rocket as well) from the perihelion until the distance to the Sun makes it worth to jettison the sail (maybe reorient the mirrors towards solar panels) and make the rest of the delta-v on ion engines powered by the solar panels increasingly replaced by a set of dedicated RTGs.

There is also a book called Project Orion: The True Story of the Atomic Spaceship. It's still sitting on my shelf, but I don't remember it being a particularly inspiring read because it was tailored towards interstellar travel when we hadn't even reached Mars yet.

Similarly crazy idea, https://en.wikipedia.org/wiki/Nike_Hercules A nuclear tipped SAM, blow all the missiles out of the sky together with the sky

Related, Sprint missile test (anti-ballistic-missile missile). Extremely fast acceleration, you can see in the test footage which is not sped up.

Mass: 7,700 lbs.; Thrust: 650,000 lbs.

Around 100 G of acceleration, reaching Mach 10 within 5 seconds.

"The first stage was exhausted after only 1.2 seconds, but produced 650,000 pounds-force (2,891 kilonewtons) of thrust. On separation, the spent first stage disintegrated due to aerodynamic forces. The second stage fired within 1 to 2 seconds of launch. Interception at an altitude of 1 to 19 miles (1.5 to 30 km) took at most 15 seconds." https://en.m.wikipedia.org/wiki/Sprint_(missile)

https://youtu.be/kvZGaMt7UgQ

Nuclear tipped SAM isn't too crazy for the time. They were defending against nuclear-armed supersonic bombers and knocking out multiple with one missile was good idea. Early SAMs also weren't that good.

There were lots of nuclear tactical weapons (some bonkers) at the time. Nuclear torpedos. Nuclear anti-submarine rockets. Nuclear artillery shells. Nuclear tactical rockets.

The Russians still have theirs.

https://en.wikipedia.org/wiki/A-135_anti-ballistic_missile_s...

And well, the Genie missile of course https://en.wikipedia.org/wiki/AIR-2_Genie

> Like almost any thorny military problem of the 1950s, the solution was the application of nuclear bombs.

Magnificent.

Project Orion is a really bad idea. I guess it could be a good idea in specific situation where have to get a lot of mass off the planet and don't care about the effects.

Problem one is that detonating a series of nuclear bombs in the atmosphere. The first couple are close to the ground and produce local fallout, the higher ones produce global fallout.

Problem two is that detonating nuclear bombs in space causes EMP. That doesn't destroy electronics on ground as thought but will knock out the electrical grid. The extra radiation will knock out satellites in space.

There is interstellar Orion, Project Daedalus, but that is quite different with inertial confinement fusion and magnetic fields directing the exhaust.

Launching from lunar orbit would obviate EMP and terrestrial radiation concerns.

But those are the least of the concerns.

The problem with that is Orion is that it is heavy. It only makes sense when launching the whole thing from the ground. Orion has been proposed for interplanetary propulsion since it is pretty efficient. But would need to be convertible from ground-launch to space propulsion. Nuclear rockets are pretty good and safer to launch.

The other problem is that nuclear weapons are expensive. Something like Davy Crockett is 2kg of plutonium, and mid-sized Orion would use 800 to get to orbit. Plutonium is $4000/g which means $6.4 billion to launch Orion. Orion that puts 1600t in orbit. Or 10 Starships which is less as disposable rockets and way less if reuasable.

In 1965 the Atomic Energy Commission put the cost of plutonium 239 at $10/gram, which by simple consumer price indexing (only a rough guide, admittedly) would make it $96/gram today.

See Table I in this publication "Values In Spent Fuel From Power Reactors":

https://www.osti.gov/servlets/purl/4618921

At $96 per gram instead of $4000, that's a much more attractive $154 million to put 1600 tons in orbit. Uranium enrichment costs have fallen greatly since the 1960s as centrifuges have replaced gaseous diffusion, so uranium-fueled units would probably cost less (despite the greater mass of uranium required).

I'd say that the main modern problems of a terrestrially launched Orion are treaty violations and giving a plausible cover for nations to again pursue developing "peaceful" nuclear explosives.

Not as "spicy" an idea as the Nuclear saltwater rocket however, which instead of discrete bombs involves dissolving a load of bomb-grade fissiles into water and then ejecting them out a conventional rocket engine, with the idea the solution goes critical somewhere in the vincinity of the exhaust nozzle. Now if you're thinking "Does that replace singular discrete nuclear explosions with a continual nuclear explosion shrouded in an expanding cloud of radioactive superheated steam?", the answer is yes, yes it does.

Weirdest thing is the design doesn't actually have as much potential ISP as a pulsed detonation system like an Orion, despite being a bonafide torchship. Go figure

https://en.m.wikipedia.org/wiki/Nuclear_salt-water_rocket

IIRC the estimate was that the extra radiation from a launch would kills tens of people per launch, not thousands. Still not great (especially if you are one of those victims), but not as much as you might expect.

Another problem with it is that, unlike an ordinary rocket engine, it cannot be tested on a test stand. The injection of nuclear units, as well as the interaction of the unit with the pusher plate, are intimately affected by the surrounding environment (all that hot gas from previous explosions in the atmosphere). Getting this thing to work reliably for launch from Earth would be a nightmare.

It might be easier to test the engine in space, say with an upside down unit on the Moon.

It wasn't as bad as you would expect. The total fallout on Earth from a launch would have been about the same as a single 10 Megaton air burst, which we were doing all the time back then.

Relevant xkcd: https://xkcd.com/2423/

Ah this is the project that the show Ascension[1] was based on

1. https://m.imdb.com/title/tt3696720/

I sorta hope they literally did what they did in Ascension IRL, does anyone else?

it was a fun plot point of the Remembrance of Earth's Past trilogy (Three Body Problem) too

Exactly, it's quite important for the plot of "Death's End"