# Could I build a NUCLEAR powered hot air ballon? **URL:** \ **Category:** Factual Questions\ **Created:** [October 15, 2006, 12:59am UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473 "2006-10-15T00:59:33Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Ranchoth](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranchoth/32/1066_2.png) [@Ranchoth](https://boards.straightdope.com/u/Ranchoth)\ **Post date:** [October 15, 2006, 12:59am UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/1 "2006-10-15T00:59:33Z")
I was watching one of the Discovery channels the other night, when they had a documentary on ballooning. Specifically, long distance (and round-the-world) balloon flights. They mentioned that it was basically impossible to circumnavigate the Earth in a pure hot air balloon because there’s no way to carry enough fuel for the entire trip. That got me thinking: naturally, that would apply to _conventional_ fuels, like gas or oil…but what about _un_conventional sources? So I come to my question: Is there any way to use a _nuclear_ energy source (such as a [Radioisotope Thermoelectric Generator](http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator)) to power a hot air balloon (Either by directly heating the air, or powering an electrical heating system)? My only requirments would be that it be small enough to fit on a craft roughly the size of a normal balloon or thermal airship (say, [url=[Breitling Orbiter - Wikipedia](http://en.wikipedia.org/wiki/Breitling_Orbiter)]“Breitling Orbiter” size, max.), and that the radiation not kill the crew. (And preferably not badly irradiate the _rest_ of the world as it flew, but that’s technically not a deal breaker.) So…any thoughts? ---
**Author:** ![Tripler](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/tripler/32/21807_2.png) [@Tripler](https://boards.straightdope.com/u/Tripler)\ **Post date:** [October 15, 2006, 1:38am UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/2 "2006-10-15T01:38:06Z")
So, I’m sitting here with my girlfriend, and was about to impress her with my badass knowledge of like, “Well, yeah, you know. . . NASA and the Air Force tried building a [nuclear-powered missile](http://www.merkle.com/pluto/pluto.html) . . .” The big problem with this is the fallout from the reactor itself. Granted, the SLAM vented hot friggin’ magma of Uranium out, thus leaving a trail of fallout wherever it went. I would think this hot air balloon would do the same. Plus, what if it came down rather uncontrolled? Tripler I’m going to venture a vote of “Possible, but not practical.” ---
**Author:** ![treis](https://avatars.discourse-cdn.com/v4/letter/t/bc79bd/32.png) [@treis](https://boards.straightdope.com/u/treis)\ **Post date:** [October 15, 2006, 2:48am UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/3 "2006-10-15T02:48:44Z")
[QUOTE=Ranchoth] I was watching one of the Discovery channels the other night, when they had a documentary on ballooning. Specifically, long distance (and round-the-world) balloon flights. They mentioned that it was basically impossible to circumnavigate the Earth in a pure hot air balloon because there’s no way to carry enough fuel for the entire trip. That got me thinking: naturally, that would apply to _conventional_ fuels, like gas or oil…but what about _un_conventional sources? So I come to my question: Is there any way to use a _nuclear_ energy source (such as a [Radioisotope Thermoelectric Generator](http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator)) to power a hot air balloon (Either by directly heating the air, or powering an electrical heating system)? My only requirments would be that it be small enough to fit on a craft roughly the size of a normal balloon or thermal airship (say, [url=[Breitling Orbiter - Wikipedia](http://en.wikipedia.org/wiki/Breitling_Orbiter)]“Breitling Orbiter” size, max.), and that the radiation not kill the crew. (And preferably not badly irradiate the _rest_ of the world as it flew, but that’s technically not a deal breaker.) So…any thoughts? [/QUOTE] I’m thinkig that it’s unlikely. A nuclear reactor requires a metric ass load of water to cool it. That means it’s pretty tough to make a mobile one, unless you happen to be conviently moving across a large body of water. ---
**Author:** ![St\_Ides](https://avatars.discourse-cdn.com/v4/letter/s/ccd318/32.png) [@St\_Ides](https://boards.straightdope.com/u/St_Ides)\ **Post date:** [October 15, 2006, 5:01am UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/4 "2006-10-15T05:01:17Z")
Definitely a big no for those RTGs. To get a balloon up, you’re looking at a LOT more heat than one of those can provide. The burners on a baloon put out 10-15,000,000 BTUs apiece… The biggest RTG on Wikipedia there puts out 7000 BTUs at it’s absolute peak. You’re definitely not going to find a nuclear option that could fit in to a payload the size of a normal basket, and put out the neccessary heat… If you want unconventional, check out [Solar Hot Air Balloons](http://perso.orange.fr/ballonsolaire/en-index.htm). ---
**Author:** ![Paul\_in\_Qatar](https://avatars.discourse-cdn.com/v4/letter/p/ccd318/32.png) [@Paul\_in\_Qatar](https://boards.straightdope.com/u/Paul_in_Qatar)\ **Post date:** [October 15, 2006, 6:37am UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/5 "2006-10-15T06:37:24Z")
To get the maximum lift from your nuclear power source, you could use the ultimate lifting gas, very hot hydrogen. Then hang your power unit from the gondola from a very long extension cord to minimize the need for shielding. Of course hot hydrogen, like a balloon dangling a reactor at the end of 100M of rope, presents a slew of engineering hurtles. Could it be done, I guess. Easily? Probably not. ---
**Author:** ![groman](https://avatars.discourse-cdn.com/v4/letter/g/73ab20/32.png) [@groman](https://boards.straightdope.com/u/groman)\ **Post date:** [October 15, 2006, 8:07am UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/6 "2006-10-15T08:07:23Z")
It might be possible, but entirely impractical to create a very dangerously unshielded hot air balloon that maintained air temperature through convecting air directly through some sort of a radiator attached to a smaller reactor such as [http://en.wikipedia.org/wiki/Aircraft\_Reactor\_Experiment](http://en.wikipedia.org/wiki/Aircraft_Reactor_Experiment) Of course you couldnt’ fly it since without the shielding you would fry. ---
**Author:** ![Quartz](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/quartz/32/267_2.png) [@Quartz](https://boards.straightdope.com/u/Quartz)\ **Post date:** [October 15, 2006, 9:33am UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/7 "2006-10-15T09:33:36Z")
But would a RTG be sufficient to power a dirigible on Titan? That is, supply enough heat to inflate the balloon and power whatever is in the gondola beneath? ---
**Author:** ![Eleusis](https://avatars.discourse-cdn.com/v4/letter/e/f4b2a3/32.png) [@Eleusis](https://boards.straightdope.com/u/Eleusis)\ **Post date:** [October 15, 2006, 10:10am UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/8 "2006-10-15T10:10:23Z")
I love this board. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [October 15, 2006, 11:31am UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/9 "2006-10-15T11:31:31Z")
Why would you but the thermal nuke generator outside the ballon? Why not right in the center? ---
**Author:** ![Ranchoth](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ranchoth/32/1066_2.png) [@Ranchoth](https://boards.straightdope.com/u/Ranchoth)\ **Post date:** [October 15, 2006, 12:32pm UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/10 "2006-10-15T12:32:25Z")
[QUOTE=St\_Ides] To get a balloon up, you’re looking at a LOT more heat than one of those can provide. The burners on a baloon put out 10-15,000,000 BTUs apiece… The biggest RTG on Wikipedia there puts out 7000 BTUs at it’s absolute peak. [/QUOTE] Hmmm…15 million BTUs? I just ran that through an online converter, and that’s telling me that that’s equivilant to…4.3 megawatt/hours. Is that how much power I’d need to generate to create that much heat electrically, or did I completely botch the numbers? If that’s so, and if the [numbers on this page are correct (the SNAP-3 data looks legit, at least)](http://72.14.253.104/search?q=cache:jgSTzLN8W08J:sei2.sei.aero/ACDB/ACpowDB.asp+%22Advanced+concepts+database%22+snap+RTG&hl=en&gl=us&ct=clnk&cd=1&ie=UTF-8), then does look that the RTGs are definately (damnit) out, yeah—though some of the space fission reactors might work…maybe. If we’re going for a [“Solo Spirit”](http://www.pbs.org/wgbh/nova/balloon/factsheetsf.html) type balloon, which already carried 3000 lbs of fuel. ---
**Author:** ![Rick](https://avatars.discourse-cdn.com/v4/letter/r/9f8e36/32.png) [@Rick](https://boards.straightdope.com/u/Rick)\ **Post date:** [October 15, 2006, 2:18pm UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/11 "2006-10-15T14:18:16Z")
What about a [pebble bed reactor?](http://en.wikipedia.org/wiki/Pebble_bed_reactor) using a fresh air intake, and the heated air directed into the ballon. Hang your basket far enough below the reactor and radiation is not a problem. You would need some type of ducting system to dump excess hot air when the ballon is full. The Eviromental Impact Report will be left as an exercise for the student. ---
**Author:** ![DanBlather](https://avatars.discourse-cdn.com/v4/letter/d/f4b2a3/32.png) [@DanBlather](https://boards.straightdope.com/u/DanBlather)\ **Post date:** [October 15, 2006, 4:32pm UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/12 "2006-10-15T16:32:06Z")
[QUOTE=kanicbird] Why would you but the thermal nuke generator outside the ballon? Why not right in the center? [/QUOTE] And then make the balloon skin out of very thin lead foil to shield you from radiation. It would be a (drum roll) lead balloon. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [October 15, 2006, 5:18pm UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/13 "2006-10-15T17:18:42Z")
I think it can be done, but by taking liberties with the working fluid outside the ballon. The easiest way is to use water instead of air, then a nuke powered sub might even qualify. If we are to stay with a gas as the working fluid, then if we move from earth to a gas giant with a very dense atmosphere a nuke powered ballon might not only work, but might one day be used for exploring those places. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [October 15, 2006, 7:59pm UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/14 "2006-10-15T19:59:59Z")
Myself, I’m going to instead look at the balloon membrane. If we make the membrane a sufficiently good insulator, we can use an arbitrarily low power to heat the air inside the balloon. I don’t know what the current materials limits are for insulating membranes, but I don’t think there’s any inherent upper bound. ---
**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 15, 2006, 8:21pm UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/15 "2006-10-15T20:21:48Z")
[QUOTE=treis] I’m thinkig that it’s unlikely. A nuclear reactor requires a metric ass load of water to cool it. That means it’s pretty tough to make a mobile one, unless you happen to be conviently moving across a large body of water. [/QUOTE] The OP wasn’t asking about a nuclear reactor. He was talking about a [Radioisotope Thermoelectric Generator](http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator), which doesn’t require any working fluid. Also, nuclear reactors themselves do not necessarily require water to cool them. Water just happens to be generally very convenient. The biggest problem with any nuclear power source is the weight of the shielding that would be required. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [October 16, 2006, 2:54am UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/16 "2006-10-16T02:54:30Z")
[QUOTE=Chronos] I don’t know what the current materials limits are for insulating membranes, but I don’t think there’s any inherent upper bound. [/QUOTE] Vacuum? ---
**Author:** ![Der\_Trihs](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/der_trihs/32/233_2.png) [@Der\_Trihs](https://boards.straightdope.com/u/Der_Trihs)\ **Post date:** [October 16, 2006, 8:50am UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/17 "2006-10-16T08:50:49Z")
[QUOTE=Ranchoth] So I come to my question: Is there any way to use a _nuclear_ energy source (such as a [Radioisotope Thermoelectric Generator](http://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator)) to power a hot air balloon (Either by directly heating the air, or powering an electrical heating system)? [/QUOTE] IIRC those are too low powered. Perhaps a [quantum nucleonic reactor](http://www.newscientist.com/article.ns?id=dn3406), which the Air Force has been considering for use in drones. If nothing else, it has a cool name. 🙂 > [@](#): > > Instead of a conventional fission reactor, it is focusing on a type of power generator called a quantum nucleonic reactor. This obtains energy by using X-rays to encourage particles in the nuclei of radioactive hafnium-178 to jump down several energy levels, liberating energy in the form of gamma rays. A nuclear UAV would generate thrust by using the energy of these gamma rays to produce a jet of heated air. > > The military interest was triggered by research published in 1999 by Carl Collins and colleagues at the University of Texas at Dallas. They found that by shining X-rays onto certain types of hafnium they could get it to release 60 times as much energy as they put in (New Scientist print edition, 3 July 1999). > > Tightly controlled reaction > The reaction works because a proportion of the hafnium nuclei are “isomers” in which some neutrons and protons sit in higher energy levels than normal. X-ray bombardment makes them release this energy and drop down to a more stable energy level. > > So the AFRL has since been looking at ways in which quantum nucleonics could be used for propulsion. “Our directorate is being cautious about it. Right now they want to understand the physics,” says Christopher Hamilton at the Wright Patterson Air Force Base in Ohio, who conducted the latest nuclear UAV study. > > The AFRL says the quantum nucleonic reactor is considered safer than a fission one because the reaction is very tightly controlled. “It’s radioactive, but as soon as you take away the X-ray power source its gamma ray production is reduced dramatically, so it’s not as dangerous [as when it’s active],” says Hamilton. > > Paul Stares, an analyst with the US Institute of Peace in Washington DC, wonders what would happen if a nuclear UAV crashed. But Hamilton insists that although hafnium has a half-life of 31 years, which according to Britain’s National Radiological Protection Board is equivalent to the highly radioactive caesium-137, the structural composition of hafnium hinders the release of this radiation. > > “It’s probably something you would want to stay away from but it’s not going to kill you,” claims Hamilton. ---
**Author:** ![Malacandra](https://avatars.discourse-cdn.com/v4/letter/m/45deac/32.png) [@Malacandra](https://boards.straightdope.com/u/Malacandra)\ **Post date:** [October 16, 2006, 9:03am UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/18 "2006-10-16T09:03:33Z")
[QUOTE=DanBlather] And then make the balloon skin out of very thin lead foil to shield you from radiation. It would be a (drum roll) lead balloon. [/QUOTE] Why stop at a balloon when you can make a dirigible? Can’t think what you’d call it though… :smack: ---
**Author:** ![Hypno-Toad](https://avatars.discourse-cdn.com/v4/letter/h/b2d939/32.png) [@Hypno-Toad](https://boards.straightdope.com/u/Hypno-Toad)\ **Post date:** [October 16, 2006, 6:32pm UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/19 "2006-10-16T18:32:34Z")
[QUOTE=Malacandra] Why stop at a balloon when you can make a dirigible? Can’t think what you’d call it though… :smack: [/QUOTE] Jefferson Airship? ---
**Author:** ![Cluricaun](https://avatars.discourse-cdn.com/v4/letter/c/bb73d2/32.png) [@Cluricaun](https://boards.straightdope.com/u/Cluricaun)\ **Post date:** [October 16, 2006, 7:12pm UTC](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473/20 "2006-10-16T19:12:50Z")
[QUOTE=Hypno-Toad] Jefferson Airship? [/QUOTE] No, the New, New Yardbirds. [Next page](https://boards.straightdope.com/t/could-i-build-a-nuclear-powered-hot-air-ballon/376473.md?page=2)