# Is this possible? (nuclear propulsion) **URL:** \ **Category:** Factual Questions\ **Created:** [April 10, 2003, 11:20am UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750 "2003-04-10T11:20:36Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![starman](https://avatars.discourse-cdn.com/v4/letter/s/8c91f0/32.png) [@starman](https://boards.straightdope.com/u/starman)\ **Post date:** [April 10, 2003, 11:20am UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/1 "2003-04-10T11:20:36Z")
Is [this](http://spacedaily.com/news/rocketscience-03l.html) possible? How do you compress the solid fissile material to a “supercritical” state? If this is possible, then it could greatly aid Solar System exploration. -Oli ---
**Author:** ![UncleBill](https://avatars.discourse-cdn.com/v4/letter/u/d26b3c/32.png) [@UncleBill](https://boards.straightdope.com/u/UncleBill)\ **Post date:** [April 10, 2003, 11:33am UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/2 "2003-04-10T11:33:07Z")
From your cite. > [@](#): > > Andrews Space & Technology (AS&T) successfully demonstrated the fundamental operating principles of a propulsion system… > > AS&T tested the Company’s Mini-Mag Orion propulsion concept by completing two **magnetic compression technology** experiments in the world’s largest pulse power machine… > > AS&T successfully verified the process of compressing solid matter to high densities **in an electromagnetic field** … Sure sounds like they have the basics licked. Now to get the system small enough to fly… ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [April 10, 2003, 11:37am UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/3 "2003-04-10T11:37:47Z")
I don’t know about this particular manifestation of the program, but there certainly was a lot of work on nuclear propulsion in 1958-1959 on Project Orion. I’ve heard about that for years, but am finally learning more about it now – I’m reading **Project Orion: The True Story of the Atomic Spaceship** by George Dyson (Freeman Dyson’s son). It’s fascinating reading. There was a huge amount of theoretical work done on this, and the prospects were tremendous – you could cross the solar system in a month using small atomic bombs thrust out of the back of the ship (which would be immense). Larry Niven and Jerry Poyrnelle used the idea in their novel **Footfall**. The biggest problem was apparently fallout. I have no idea how the present scheme intends to get around that. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [April 10, 2003, 11:54am UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/4 "2003-04-10T11:54:18Z")
What is a _simulated_ fissile material (the way that they write it sounds like they mean something quite different from ‘a simulation of magnetic compression of a fissile material’) ---
**Author:** ![starman](https://avatars.discourse-cdn.com/v4/letter/s/8c91f0/32.png) [@starman](https://boards.straightdope.com/u/starman)\ **Post date:** [April 10, 2003, 11:56am UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/5 "2003-04-10T11:56:54Z")
I believe the idea is not to use the nuclear “pulses” until the craft is well out of the atmsphere. The bit I do not understand is how they intend to compress a few grams of fissile material (uranium or plutonium I guess) to “supercritical” point. In a ‘normal’ nuclear explosive, convential explosives are utilised to bring two hemispheres of fissile material together, thus acheiving critical mass. In this case, it sounds like the masses of fissile material are well below critical mass. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [April 10, 2003, 12:04pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/6 "2003-04-10T12:04:49Z")
There has just been a documentary on British TV about this very subject- the project was already quite advanced before any astronauts even got into space in 1961- but was abandoned for political reasons to do with nuclear proliferation in space. Kennedy (I think it was) put the lid on it, favouring chemical rockets instead for the Moon program. The other problem is getting vast amounts of fissile material into orbit without any disasters, which could potentially cause a lot of fallout. However, if this new design is sucessful it could be used well above the atmosphere, and preferably away from the Earth altogether, and it should be very useful as an interplanetary motor. I still imagine that a fusion drive of some sort is the thing to go for in the longer term. * * * Sci-fi worldbuilding at [http://www.orionsarm.com/](http://www.orionsarm.com/) ---
**Author:** ![DreadCthulhu](https://avatars.discourse-cdn.com/v4/letter/d/db5fbb/32.png) [@DreadCthulhu](https://boards.straightdope.com/u/DreadCthulhu)\ **Post date:** [April 10, 2003, 12:33pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/7 "2003-04-10T12:33:38Z")
Well, once you get out of the earths atmosphere, fallout isn’t a problem - space is already full of radiation anyways, and the thrust of this thing would be a drop in the ocean compared to whats out there. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [April 10, 2003, 1:08pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/8 "2003-04-10T13:08:03Z")
> [@](#): > > Well, once you get out of the earths atmosphere, fallout isn’t a problem - space is already full of radiation anyways, and the thrust of this thing would be a drop in the ocean compared to whats out there. Granted, but that’s not the issue – you’d have to use quite a few bombs (under the old Orion program, at any rate) just to clear the atmosphere, and those are the ones that cause problems. Heck, it’s not just the fallout – Project Orion test firings of a miniature test vehicle “fueled” by C-4 drew a lot of complaints back in 1958. Nuclear firing would make a helluva bang. Then there’s the EMP issue (which would continue even out of the atmosphere), etc. Maybe this new magnetic compression technology won’t have some of these problems, but if it’s still relying on fission explosions for the propulsive force, I can’t see how they can be avoided. ---
**Author:** ![starman](https://avatars.discourse-cdn.com/v4/letter/s/8c91f0/32.png) [@starman](https://boards.straightdope.com/u/starman)\ **Post date:** [April 10, 2003, 1:19pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/9 "2003-04-10T13:19:31Z")
Not necessarily. The craft could be launched by chemical boosters, only to deploy the nuclear propulsion system once in space. ---
**Author:** ![rexnervous](https://avatars.discourse-cdn.com/v4/letter/r/e9c0ed/32.png) [@rexnervous](https://boards.straightdope.com/u/rexnervous)\ **Post date:** [April 10, 2003, 1:57pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/10 "2003-04-10T13:57:36Z")
> [@](#): > > \*Originally posted by starman \* > \*\*Not necessarily. The craft could be launched by chemical boosters, only to deploy the nuclear propulsion system once in space. \*\* But you’d have to be far enough away not to fry the satellites with the EMP. Any ideas how far an EMP would travel in space? ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [April 10, 2003, 2:02pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/11 "2003-04-10T14:02:18Z")
Drops off as the inverse square of the radius (1/r^2), but range-wise it would be infinite. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [April 10, 2003, 2:14pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/12 "2003-04-10T14:14:40Z")
> [@](#): > > ## quote: > > ## Originally posted by starman Not necessarily. The craft could be launched by chemical boosters, only to deploy the nuclear propulsion system once in space. > > But you’d have to be far enough away not to fry the satellites with the EMP. Any ideas how far an EMP would travel in space? > [@](#): > > Drops off as the inverse square of the radius (1/r^2), but range-wise it would be infinite. 1.) I don’t know the size of the neo-Orion craft, but in the case of the 1958-vintage Orion, chemical boosters wouldn’t have done it. That ship was _huge_ — 4,000 _tons_. 2.) EMP on earth, as I understand it, is due to recombination of ionized gases from the initial explosion. EMP in space is due to interaction of the explosion with the earth’s magnetic field. Once you get to a point where the magnetic field has fallen off significantly, I think you can ignore EMP as a major force. (This is all based on my dim recollection of a Scientific American article on this circa a decade ago). Of course, the main dipole radiation of an EMP will die off as the inverse square of the distance, wherever the EMP is generated in the first place. ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [April 10, 2003, 11:12pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/13 "2003-04-10T23:12:15Z")
> [@](#): > > \*Originally posted by starman \* > The bit I do not understand is how they intend to compress a few grams of fissile material (uranium or plutonium I guess) to “supercritical” point. > In a ‘normal’ nuclear explosive, convential explosives are utilised to bring two hemispheres of fissile material together, thus acheiving critical mass. In this case, it sounds like the masses of fissile material are well below critical mass. The thing is that what is usually defined as the “critical mass” is the mass necessary to sustain a chain reaction at standard temperature and **pressure**. If you can compress the nuclear explosive to densities significantly above those in a normal bomb, you can get nuclear explosions with masses (and yields) lower than those associated with simple weapons. This seems to be the idea behind the proposal, using EM technology to do this compression. There seem to me two unanswered questions. The first is that it was a key aspect of Orion that the bombs went off **behind** the ship. I don’t see the compression required as remotely acquirable in that configuration given current technology. You can detonate the bombs within the ship, but that’s unfavourable. The other thing is that it’s a pervasive theme in Dyson (and I second the recommendation of _Project Orion_) as a great read) that the idea scales favourably the bigger it gets. A 40 tonne Orion ship is wasteful, a 4000 tonne one “realistic”. Using small explosives and appealing to Orion seems just wrong. Incidentally, I thought the interesting aspect of the BBC4 documentary that **eburacum45** mentions, compared to Dyson’s book, was that the BBC had got an interview with Jeremy Bernstein, but that Dyson hadn’t. Noticing this probably makes me a Project Orion nerd … ---
**Author:** ![rabbit](https://avatars.discourse-cdn.com/v4/letter/r/919ad9/32.png) [@rabbit](https://boards.straightdope.com/u/rabbit)\ **Post date:** [April 11, 2003, 2:24am UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/14 "2003-04-11T02:24:03Z")
I might’ve misunderstood the reading, but I got the impression that in this case the propulsion was not acheived through the explosions pushing the craft, but rather that some sort of plasma would be created and expelled (I gather in the same way that regular ignited rocket fuel is expelled) out the back. Am I wrong? ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [April 11, 2003, 1:52pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/15 "2003-04-11T13:52:48Z")
**rabbit** is right. From the company press release [http://www.andrews-space.com/en/news/press\_releases.html](http://www.andrews-space.com/en/news/press_releases.html) > [@](#): > > The original Orion concept proposed the > use of nuclear explosives ejected behind a spacecraft to propel it to other planets. The Mini-Mag Orion > design compresses small pellets containing a few grams of simulated fissile material to beyond their > supercritical point using a magnetic field. The explosion, equivalent to five tons of TNT (several orders of > magnitude smaller than a traditional nuclear bomb), creates plasma that is directed by a magnetic nozzle > to generate vehicle thrust. This highly efficient form of nuclear propulsion can produce enough thrust at > high efficiency (specific impulse) to dramatically reduce the time required to travel between planets. ---
**Author:** ![BMalion](https://avatars.discourse-cdn.com/v4/letter/b/e274bd/32.png) [@BMalion](https://boards.straightdope.com/u/BMalion)\ **Post date:** [April 11, 2003, 2:29pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/16 "2003-04-11T14:29:38Z")
> [@](#): > > \*Originally posted by bonzer \* > \*\*…You can detonate the bombs within the ship, but that’s unfavourable… \*\* You are now unofficially nominated for the upcoming “Understatement Of The Year Award” 😉 ---
**Author:** ![Inoshiro](https://avatars.discourse-cdn.com/v4/letter/i/a9adbd/32.png) [@Inoshiro](https://boards.straightdope.com/u/Inoshiro)\ **Post date:** [April 11, 2003, 5:01pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/17 "2003-04-11T17:01:59Z")
> [@](#): > > \*Originally posted by CalMeacham \* > \*\*Granted, but that’s not the issue – you’d have to use quite a few bombs (under the old Orion program, at any rate) just to clear the atmosphere, and those are the ones that cause problems… \*\* Anyone know what the prospects are for mining fissionable materials on the moon? I would think you could build and launch quite a heavy craft (4000 tons is no big deal in lunar gravity) from the moon and people wouldn’t get too upset about fallout. You wouldn’t even need the nuclear rocket until you were clear of the moon anyway since you could launch with chemical rockets in the low gravity. Alternately, if building a ship on the moon is unfeasible we could build and launch it from earth in pieces, assemble in orbit and fly to the moon using chemical rockets to get the nuclear fuel loaded from the hypothetical lunar uranium mines. Then set off for Mars or the outer solar system. ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [April 11, 2003, 5:11pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/18 "2003-04-11T17:11:30Z")
I would imagine the cost of building, supplying and mining would dwarf any advantages you might derive from a moon minig scheme. ---
**Author:** ![MegaDave](https://avatars.discourse-cdn.com/v4/letter/m/db5fbb/32.png) [@MegaDave](https://boards.straightdope.com/u/MegaDave)\ **Post date:** [April 11, 2003, 5:43pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/19 "2003-04-11T17:43:08Z")
I read a report that stated that there is everything on the moon already that you would need to build an entire colony (i.e., building materials). So I think a big part of the ship (especially one 4000 tons) would be built in space. The amount of thrust that you would need to get to space (let alone out of Earth’s orbit) would be tremendoulsy huge in a ship that big. Grey and Rabbit have the right idea, the purpose of the nuclear explosions would not be for the impact of the explosions to propell the ship, but for the byproduct of the explosions (called plasma) to be used by forcing it out the back of the ship (yes very similar to the chemical rockets). Not only is this an effective way to get enough velocity going to take some serious time off space travel, but is also astoundingly efficient, with a ship the size mentioned above, it would be no problem carrying enough fuel to travel several human lifetimes without having to stop. Btw, I also heard of a theory where there would be small nuclear explosions set off in front of a ship (possibly several thousand yards in front) and a huge parachute type trap for the fallout. The net effect of this would be that the trap would be attatched to the ship (of course) and would pull the ship along at an ever increasing speed. ---
**Author:** ![Inoshiro](https://avatars.discourse-cdn.com/v4/letter/i/a9adbd/32.png) [@Inoshiro](https://boards.straightdope.com/u/Inoshiro)\ **Post date:** [April 11, 2003, 7:16pm UTC](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750/20 "2003-04-11T19:16:16Z")
> [@](#): > > \*Originally posted by Grey \* > \*\*I would imagine the cost of building, supplying and mining would dwarf any advantages you might derive from a moon minig scheme. \*\* Initially yes. Once the infrastructure was in place it would be largely self-sustaining. And you have a base on a low gravity world from which all sorts of ponderous craft could be launched that would literally never fly on earth. Send the crews up from earth and build the heavy stuff on the moon. After all when we talk about nuclear rockets and deep space exploration we are already talking about pretty big projects. Would setting up a moon colony really add all that much to the cost especially considering its later advantages as a low-grav launch/construction base. Of course we would need to miniaturize and spaceproof things like steel mills and smelters. Whether that can be done I don’t know. This is probably a hijack but it raises the whole interesting question of the general problems of industrializing other worlds. Particularly those like the moon and Mars that lack much atmosphere or running water (though there is hopefully water ice on both). [Next page](https://boards.straightdope.com/t/is-this-possible-nuclear-propulsion/167750.md?page=2)