# An H-bomb accelerates a metal cube in space. **URL:** \ **Category:** Factual Questions\ **Created:** [October 23, 2003, 1:43pm UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110 "2003-10-23T13:43:35Z")\ **Posts on this page:** 16\ **Page:** 1
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [October 23, 2003, 1:43pm UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/1 "2003-10-23T13:43:35Z")
My notional spacecraft is essentially a metal cube holding a number of nukes in front of it to shield them from detonations behind it. It has a nuke-launching mechanism which projects a nuke a certain distance behind it before detonation. Questions: i) What force _F_ would a large H-bomb exert per square metre of my cube in space at, say, 1 km proximity? Assuming that radiation falls off exponentially, how much _radiative_ energy _E_ would be incident per square metre? ii) What would my cube comprise (_eg_. a titanium cube with reflective shielding) in order to offer the best low-weight/high durability solution? iii) Given that the cube of (ii) has a density of _D_ kg per square metre exposed to the force _F_ of part (i), how many nukes would be required to accelerate the structure to, say, 0.1c? Also, what temperature would each cubic metre attain given its specific heat capacity and _E_? Further feasibility/modification questions to follow, perhaps. (I would research all this myself if I had time - go on, indulge me.) ---
**Author:** ![Rodd\_Hill](https://avatars.discourse-cdn.com/v4/letter/r/3ab097/32.png) [@Rodd\_Hill](https://boards.straightdope.com/u/Rodd_Hill)\ **Post date:** [October 23, 2003, 1:48pm UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/2 "2003-10-23T13:48:39Z")
[Bangs ceiling with broom handle] “What the hell are they _doing_ up there? Damn students!” ---
**Author:** ![toadspittle](https://avatars.discourse-cdn.com/v4/letter/t/c0e974/32.png) [@toadspittle](https://boards.straightdope.com/u/toadspittle)\ **Post date:** [October 23, 2003, 2:12pm UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/3 "2003-10-23T14:12:45Z")
Try searching for “orion”. Nuke-propelled spacecraft have been done to death here. ---
**Author:** ![rjk](https://avatars.discourse-cdn.com/v4/letter/r/ed655f/32.png) [@rjk](https://boards.straightdope.com/u/rjk)\ **Post date:** [October 23, 2003, 2:16pm UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/4 "2003-10-23T14:16:13Z")
I’m certainly not up for the calculations, but try a search for “Project Orion”. The idea has been around for a long time. ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [October 23, 2003, 2:41pm UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/5 "2003-10-23T14:41:11Z")
I did search this, but specific numbers (even simply for _F_) were a little scarce - I’ll have another go. ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [October 23, 2003, 4:04pm UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/6 "2003-10-23T16:04:14Z")
Still no numbers, but useful stuff. A nuke in space would produce very little force due to the tiny number of atoms involved in the explosion. A great deal of energy is produced but very little propulsion - essentially it would just be a huge fireball. From [Caltech Q&A](http://spider.ipac.caltech.edu/staff/waw/mad/mad12.html): > [@](#): > > There is one account of a nuclear explosion in the public literature that I know, that of the 1 Megaton “Starfish” explosion in 1962 over Johnston Is. in the South Pacific. Because it was not really in space, but in the upper atmosphere a few hundred km high, it created a ghostly fireball hundreds of km in extent, much less brilliant than in air, but still “a fearsome sight” (according to Bernard J. O’Keefe, “Nuclear Hostages”, 1983). So, the energy must be transferred to some kind of propellant which pushes on, say, a concave push plate. From the [best source I found](http://www.astronautix.com/articles/probirth.htm): > [@](#): > > A useful figure for comparing rocket engines is specific impulse (Isp), defined as pounds of thrust produced per pound of propellant consumed per second. The units of Isp are thus seconds. The best chemical rocket in service, the cryogenic hydrogen-oxygen engine, has an Isp of about 450 seconds > … > Taylor adopted Ulam’s pusher-plate idea but instead of the propellant disks he combined propellant and bomb into a single pulse unit. The propellant material of choice was plastic, probably polyethylene (15). There are indications that a plastic similar to Styrofoam is used inside hydrogen bombs to “channel” the energy from the atomic trigger into the fusible material (16). The advantage of the pusher plate design, as Taylor and Dyson saw it, was that it could simultaneously produce high thrust with high exhaust velocity. No other known propulsion system combined these two highly desirable features. The effective Isp could theoretically be as high as 10,000 to one million seconds ( **bloody hellfire!** ). The calculated force exerted on the pusher plate was immense; it would have created intolerable acceleration for a manned vehicle. > … > The expanding plasma bubble of each explosion could have a temperature of several tens of thousands of Kelvins even when the explosion occurred hundreds of feet from the plate…A scheme was devised to spray grease (probably graphite-based) onto the plate between blasts (20)…The duration of high temperatures was so short that very little heat flowed into the plate; active cooling was apparently considered unnecessary. The experimenters concluded that either aluminum or steel would be durable enough to act as plate material. (Expletive mine) Apologies for the long quote, but it appears that all of the engineering difficulties were solved long ago, and the only remaining barriers to genuine space travel of this kind stem from International Treaty violation and environmental risk inherent in the transportation of fissile materials into space. ---
**Author:** ![Exapno\_Mapcase](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/exapno_mapcase/32/1051_2.png) [@Exapno\_Mapcase](https://boards.straightdope.com/u/Exapno_Mapcase)\ **Post date:** [October 23, 2003, 4:24pm UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/7 "2003-10-23T16:24:06Z")
Freeman Dyson’s son, George, recently published [Project Orion: The True Story of the Atomic Spaceship](http://www.amazon.com/exec/obidos/tg/detail/-/0805072845/qid=1066926779/sr=1-1/ref=sr_1_1/104-2171110-1070335?v=glance&s=books). ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [October 23, 2003, 8:56pm UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/8 "2003-10-23T20:56:57Z")
Here’s an updated version of a link on Project Orion that I posted in another thread just a couple of days ago: > **[Project Orion](https://www.daviddarling.info/encyclopedia/O/OrionProj.html)** > > Project Orion, in the 1960s, examined the feasibility of building a nuclear-pulse rocket powered by nuclear fission. ---
**Author:** ![DreadCthulhu](https://avatars.discourse-cdn.com/v4/letter/d/db5fbb/32.png) [@DreadCthulhu](https://boards.straightdope.com/u/DreadCthulhu)\ **Post date:** [October 23, 2003, 9:48pm UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/9 "2003-10-23T21:48:11Z")
> [@](#): > > \*Originally posted by SentientMeat \* > \*\* > > Apologies for the long quote, but it appears that all of the engineering difficulties were solved long ago, and the only remaining barriers to genuine space travel of this kind stem from International Treaty violation and environmental risk inherent in the transportation of fissile materials into space. \*\* Of course, you could just use the nukes on the surface to lift you into orbit, thus negating the use of unreliable and expensive chemical rockets to get the vehical into orbit, as well as allowing you to build one huge-ass spaceship here on earth, with no need for special construction materials- you could probably build it in a shipyard. Of course, a ground lauch would put some extra fallout into the atmosphere, and really piss off various enviroment groups, but I consider the second part a bonus. ---
**Author:** ![bbeaty](https://avatars.discourse-cdn.com/v4/letter/b/c0e974/32.png) [@bbeaty](https://boards.straightdope.com/u/bbeaty)\ **Post date:** [October 24, 2003, 12:31am UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/10 "2003-10-24T00:31:58Z")
> [@](#): > > \*Originally posted by DreadCthulhu \* > \*\*Of course, you could just use the nukes on the surface to lift you into orbit, thus negating the use of unreliable and expensive chemical rockets to get the vehical into orbit, \*\* The Orion book mentioned that they calculated how high they’d have to turn on the nuke pulses to avoid blinding any observers. it was ~50 miles up. Unless you can put your launch site in the center of an uninhabited desert, the very sight of the “exhaust” is dangerous. (Imagine desert animals with hundreds of little dead spots burned into their retinas.) ---
**Author:** ![bump](https://avatars.discourse-cdn.com/v4/letter/b/7c8e57/32.png) [@bump](https://boards.straightdope.com/u/bump)\ **Post date:** [October 24, 2003, 2:01am UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/11 "2003-10-24T02:01:37Z")
Here’s a website from NASA that talks about Orion type systems. [http://www.islandone.org/APC/Nuclear/09.html](http://www.islandone.org/APC/Nuclear/09.html) ---
**Author:** ![Ficer67](https://avatars.discourse-cdn.com/v4/letter/f/c57346/32.png) [@Ficer67](https://boards.straightdope.com/u/Ficer67)\ **Post date:** [October 24, 2003, 9:13am UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/12 "2003-10-24T09:13:19Z")
Project Orion was a foolish project. No-one would ever actually go for a launch. The only point that Orion served was as a Think-Tank for better projects. Consider using a laser to super heat the air underneath a space-craft. This is a more modern variant of the orion project, and it has much more potential and better likelyhood of becoming a reality. ---
**Author:** ![Cerowyn](https://avatars.discourse-cdn.com/v4/letter/c/82dd89/32.png) [@Cerowyn](https://boards.straightdope.com/u/Cerowyn)\ **Post date:** [October 24, 2003, 10:05am UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/13 "2003-10-24T10:05:59Z")
> [@](#): > > \*Originally posted by Ficer67 \* > \*\*Consider using a laser to super heat the air underneath a space-craft. This is a more modern variant of the orion project, and it has much more potential and better likelyhood of becoming a reality. \*\* I’m thinking that this method of propulsion isn’t too useful on a “space-craft.” Perhaps for a launch vehicle, at least to get it into LEO. Using fusion bombs to accelerate a vessel obviously has the problem of extreme impulse to over-come, but isn’t an inherently flawed idea (assuming you only use the drive for extra-atmospheric propulsion). Of course, using a reactor to provide power some form of high-thrust ion drive would be a much better use of nuclear technology for space travel. (Current ion drives have a very high exhaust velocity, but very low impulse. That makes them desirable for very long trips, where the constant acceleration can eventually overcome their slow start.) ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [October 24, 2003, 10:22am UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/14 "2003-10-24T10:22:21Z")
Finally found a number. From [here](http://www.islandone.org/Propulsion/ProjectOrion.html), Dyson predicted an acceleration of 30 m/s/s for each nuke for a medium or large craft capable of storing thousands of nukes. (This being well _within_ human tolerance). 0.1c (30 million m/s) would therefore require one million nukes, and at one nuke release every ten seconds it would attain this speed in 10 million seconds (3.8 months). Unfortunately, the mass of a million nukes would presumably lower this acceleration figure, thus requiring _more_ nukes. However, a craft weighing one tonne per nuke appears entirely possible. So, as the nukes gradually become depleted as the journey progresses, it seems entirely feasible to build a craft capable of accelerating to 0.1c within a matter of months, thus reaching Alpha Centauri in 44 years. (How you _stop_ is a whole new problem, even if a tiny capsule is ejected. You’d best hope someone os expecting you!) ---
**Author:** ![SentientMeat](https://avatars.discourse-cdn.com/v4/letter/s/43a26b/32.png) [@SentientMeat](https://boards.straightdope.com/u/SentientMeat)\ **Post date:** [October 24, 2003, 10:38am UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/15 "2003-10-24T10:38:42Z")
Actaully, _erratum_ for my last post: Dyson predicted an _increasein velocity_ of 30 m/s for each nuke, but this acceleration would occur over less than a second, perhaps _much_ less, possibly resulting in a brief but **fatal** acceleration. ---
**Author:** ![Grey](https://avatars.discourse-cdn.com/v4/letter/g/b782af/32.png) [@Grey](https://boards.straightdope.com/u/Grey)\ **Post date:** [October 24, 2003, 11:59am UTC](https://boards.straightdope.com/t/an-h-bomb-accelerates-a-metal-cube-in-space/209110/16 "2003-10-24T11:59:14Z")
Use a magnetic sail to decelerate.