7 ms·

Silhouettes of the bomb: what can we learn from the shapes of atomic weapons?

86 points by rdl 11y ago

mirimir 11y ago
Cool :) But also see Rapatronic photographs, at <10ns after detonation: http://www.freerepublic.com/focus/f-chat/3104424/posts http://www.freerepublic.com/focus/f-chat/3104424/posts
rdl 11y ago
Relatedly, I find it deeply troubling at some level to know that the exact shape of the Earth (specifically, mass and magnetic distribution) is highly classified, since it's important to ICBM guidance.
- marklyon 11y ago
  Doesn't ITRF2008 and (to a lesser extent) WGS-84 give you what you want?
- wyager 11y ago
  Source? I'd like to read about this.
  - teh_klev 11y ago
    Could be something to do with this: http://nsarchive.gwu.edu/NSAEBB/NSAEBB509/ http://nsarchive.gwu.edu/NSAEBB/NSAEBB509/ "NASA's Applications Satellites and National Security Requirements: NASA planned on launching the Geodynamics Experimental Ocean Satellite-3 (GEOS-3) with a radar altimeter whose data would generate more accurate gravity models than any measuring devices previously flown. The data would be used to meet civilian requirements and by the U.S. Navy to improve the accuracy of its submarine-launched ballistic missiles (SLBMs). Because it also had the potential to be used by the Soviets for the same purpose, the DoD requested NASA to encrypt the data, limit the acquisition of data over the ocean areas where Soviet ballistic missile submarines operated, or delay the planned April 1975 launch until the issue could be resolved. It also requested encryption of the data from the even more capable radar altimeter planned for SEASAT-A. NASA rejected these requests but quickly agreed to restrict the dissemination of the GEOS-3 data collected over the regions where Soviet ballistic missile submarines operated (Document 38)." However is it still the case that NASA continue to withhold this data, or is it data collected by the NSA/NRO/et al's satellites that's considered classified?
    - 8note 11y ago
      they should be keeping that secret; good gravity models are a major part of the difference in accuracy of American missiles vs Russian ones.
      - dogma1138 11y ago
        Yes because the last thing you want is for the "soviets" to be able to hit their target. Surely them hitting instead a city near by or just using bigger nukes to compensate for lesser accuracy is a much better approach.
        hga 11y ago
        No, the more inaccurate their targeting, the harder it was for them pull off a counter-force first strike. No need to lead them into temptation.... Once they're launched, you've already lost catastrophicly, no matter exactly where they come down. And why the scare quotes for our adversaries who build 40,000 nuclear warheads, most of them aimed directly at us?
  - 8note 11y ago
    For important things like ICBMs, you don't want to trust easily spoofable navigation like GPS. Instead, you double integrate over the acceleration data obtained from very accurate accelerometers and gyros. since these sensors measure acceleration, and gravity is acceleration, any change in gravity over the missile's path will cause it to think it had moved differently than it did. Knowing the precise earth gravity then you can account for these changes. Changes in the magnetic field will affect compass readings, which help you decide what direction the missile is facing. Knowing the (fixed over time) change will help account for measurement error in the compass. I'm not sure how much that helps though, since the compass' earth field is constantly changing anyways due to the sun and magnetisation of the missile itself. The actual surface shape has an effect on the gravity experienced above the ground, but is also important to make sure you know what height you're aiming for, and that there's nothing in the way.
    - rdl 11y ago
      Magnetic info is sensitive more for detecting hidden equipment, like submarines.
MichaelGG 11y ago
I still don't understand how this stuff is so hard. The US pulled it off in a few years, in the 40s. Total cost of a few billion. The biggest issue is enrichment, but again, they did it within that time and budget. Several other countries/physicists were on to the same idea. Even a simple gun type with a 20kton yield is enough to severely harm a city, right? So even without the complexities of implosion or thermonuclear, it seems any dedicated actor, even a private one, should be able to pull it off. Delivery systems aside; I'd guess testing ICBMs would be difficult enough by itself. What am I missing?
- paulmd 11y ago
  You can't disregard delivery systems, that's a major piece of the picture. Nuclear bombs are most effective when airburst. If you are going to deliver by ICBM or with a military aircraft then you need an implosion design with plutonium. You might be able to sneak it in with a civilian aircraft, or via a ship or something (obviously then you can't airburst). If you want to fully open up your delivery options, you want an implosion design with plutonium. This involves running a reactor for a couple years and reprocessing the waste. And you'll have to avoid regulatory scrutiny from the IAEA to do so (which is also true of a uranium bomb). At this point the biggest problem with building a nuke of either type is getting the material. As an experiment, some college students were asked to design a nuclear weapon back in the 70s, and they apparently got it close enough that the FBI freaked out and tried to suppress their work. It would be even easier nowadays, but refining requires a lot of energy and specialized materials (eg maraging steel) that are watched really closely, and so are the materials that would be used as feedstock.
  - grkvlt 11y ago
    > some college students were asked to design a nuclear weapon Also known as the Nth Country Experiment. See https://en.wikipedia.org/wiki/Nth_Country_Experiment https://en.wikipedia.org/wiki/Nth_Country_Experiment for details, also the final report [1] is interesting. [1] http://nsarchive.gwu.edu/news/20030701/nth-country.pdf http://nsarchive.gwu.edu/news/20030701/nth-country.pdf
- Animats 11y ago
sandworm101 11y ago
"You have the long-barrels that look like gun-type designs." No. That setup was abandoned very early on, as in even before the end of WWII. The OP should have spent more time reading this https://en.wikipedia.org/wiki/Thermonuclear_weapon https://en.wikipedia.org/wiki/Thermonuclear_weapon and less time speculating.
- rdl 11y ago
  Not in artillery. It was a narrower diameter than either implosion or Teller-Ulam until probably the 70s or 80s, at which point we'd given up on nuclear artillery. (I am confident the author of the blog is knowledgeable about the US arsenal.)
  - hga 11y ago
    Fascinating; per Wikipedia, e.g. https://en.wikipedia.org/wiki/W79 https://en.wikipedia.org/wiki/W79 and https://en.wikipedia.org/wiki/W48 https://en.wikipedia.org/wiki/W48 they used a "linear implosion" technique, but it sounds like it had about the same inefficiency as the Little Boy gun assembly design. Which for safety reasons alone are iffy to field, and even more I'd imagine in a quickly accelerated artillery shell....
    - rdl 11y ago
      From reading Command and Control, a lot of the US arsenal was manifestly unsafe for a long time. Based on the number of accidents, and lack of criticality, I suspect there was some super secret design choice or design flaw which meant many classes of weapon would never go critical at all. Someone probably made the decision that only a deterrent was important, so a bunch of unsafe weapons should instead be rendered largely inert while making other gestures of readiness. I don't have any data to support that other than just the lack of unintentional nuclear detonations. http://www.amazon.com/gp/product/B00C5R7F8G/ref=dp-kindle-redirect?ie=UTF8&btkr=1 http://www.amazon.com/gp/product/B00C5R7F8G/ref=dp-kindle-re...
- GFK_of_xmaspast 11y ago
  Please consider reading about the author: http://blog.nuclearsecrecy.com/about-the-blog/ http://blog.nuclearsecrecy.com/about-the-blog/
vichu 11y ago
This brings to mind the story of John Coster-Mullen - the first person to build an accurate historical replica of Little Boy. I'd recommend reading the New Yorker article on it. It's a pretty fascinating read. http://www.newyorker.com/magazine/2008/12/15/atomic-john http://www.newyorker.com/magazine/2008/12/15/atomic-john

86 points by rdl 11y ago

Cool :) But also see Rapatronic photographs, at <10ns after detonation: http://www.freerepublic.com/focus/f-chat/3104424/posts http://www.freerepublic.com/focus/f-chat/3104424/posts

rdl 11y ago

Relatedly, I find it deeply troubling at some level to know that the exact shape of the Earth (specifically, mass and magnetic distribution) is highly classified, since it's important to ICBM guidance.

marklyon 11y ago
Doesn't ITRF2008 and (to a lesser extent) WGS-84 give you what you want?
wyager 11y ago
Source? I'd like to read about this.
- teh_klev 11y ago
  Could be something to do with this: http://nsarchive.gwu.edu/NSAEBB/NSAEBB509/ http://nsarchive.gwu.edu/NSAEBB/NSAEBB509/ "NASA's Applications Satellites and National Security Requirements: NASA planned on launching the Geodynamics Experimental Ocean Satellite-3 (GEOS-3) with a radar altimeter whose data would generate more accurate gravity models than any measuring devices previously flown. The data would be used to meet civilian requirements and by the U.S. Navy to improve the accuracy of its submarine-launched ballistic missiles (SLBMs). Because it also had the potential to be used by the Soviets for the same purpose, the DoD requested NASA to encrypt the data, limit the acquisition of data over the ocean areas where Soviet ballistic missile submarines operated, or delay the planned April 1975 launch until the issue could be resolved. It also requested encryption of the data from the even more capable radar altimeter planned for SEASAT-A. NASA rejected these requests but quickly agreed to restrict the dissemination of the GEOS-3 data collected over the regions where Soviet ballistic missile submarines operated (Document 38)." However is it still the case that NASA continue to withhold this data, or is it data collected by the NSA/NRO/et al's satellites that's considered classified?
  - 8note 11y ago
    they should be keeping that secret; good gravity models are a major part of the difference in accuracy of American missiles vs Russian ones.
    - dogma1138 11y ago
      Yes because the last thing you want is for the "soviets" to be able to hit their target. Surely them hitting instead a city near by or just using bigger nukes to compensate for lesser accuracy is a much better approach.
      - hga 11y ago
        No, the more inaccurate their targeting, the harder it was for them pull off a counter-force first strike. No need to lead them into temptation.... Once they're launched, you've already lost catastrophicly, no matter exactly where they come down. And why the scare quotes for our adversaries who build 40,000 nuclear warheads, most of them aimed directly at us?
- 8note 11y ago
  For important things like ICBMs, you don't want to trust easily spoofable navigation like GPS. Instead, you double integrate over the acceleration data obtained from very accurate accelerometers and gyros. since these sensors measure acceleration, and gravity is acceleration, any change in gravity over the missile's path will cause it to think it had moved differently than it did. Knowing the precise earth gravity then you can account for these changes. Changes in the magnetic field will affect compass readings, which help you decide what direction the missile is facing. Knowing the (fixed over time) change will help account for measurement error in the compass. I'm not sure how much that helps though, since the compass' earth field is constantly changing anyways due to the sun and magnetisation of the missile itself. The actual surface shape has an effect on the gravity experienced above the ground, but is also important to make sure you know what height you're aiming for, and that there's nothing in the way.
  - rdl 11y ago
    Magnetic info is sensitive more for detecting hidden equipment, like submarines.

MichaelGG 11y ago

I still don't understand how this stuff is so hard. The US pulled it off in a few years, in the 40s. Total cost of a few billion. The biggest issue is enrichment, but again, they did it within that time and budget. Several other countries/physicists were on to the same idea. Even a simple gun type with a 20kton yield is enough to severely harm a city, right? So even without the complexities of implosion or thermonuclear, it seems any dedicated actor, even a private one, should be able to pull it off. Delivery systems aside; I'd guess testing ICBMs would be difficult enough by itself. What am I missing?

paulmd 11y ago
You can't disregard delivery systems, that's a major piece of the picture. Nuclear bombs are most effective when airburst. If you are going to deliver by ICBM or with a military aircraft then you need an implosion design with plutonium. You might be able to sneak it in with a civilian aircraft, or via a ship or something (obviously then you can't airburst). If you want to fully open up your delivery options, you want an implosion design with plutonium. This involves running a reactor for a couple years and reprocessing the waste. And you'll have to avoid regulatory scrutiny from the IAEA to do so (which is also true of a uranium bomb). At this point the biggest problem with building a nuke of either type is getting the material. As an experiment, some college students were asked to design a nuclear weapon back in the 70s, and they apparently got it close enough that the FBI freaked out and tried to suppress their work. It would be even easier nowadays, but refining requires a lot of energy and specialized materials (eg maraging steel) that are watched really closely, and so are the materials that would be used as feedstock.
- grkvlt 11y ago
  > some college students were asked to design a nuclear weapon Also known as the Nth Country Experiment. See https://en.wikipedia.org/wiki/Nth_Country_Experiment https://en.wikipedia.org/wiki/Nth_Country_Experiment for details, also the final report [1] is interesting. [1] http://nsarchive.gwu.edu/news/20030701/nth-country.pdf http://nsarchive.gwu.edu/news/20030701/nth-country.pdf
Animats 11y ago

sandworm101 11y ago

"You have the long-barrels that look like gun-type designs." No. That setup was abandoned very early on, as in even before the end of WWII. The OP should have spent more time reading this https://en.wikipedia.org/wiki/Thermonuclear_weapon https://en.wikipedia.org/wiki/Thermonuclear_weapon and less time speculating.

rdl 11y ago
Not in artillery. It was a narrower diameter than either implosion or Teller-Ulam until probably the 70s or 80s, at which point we'd given up on nuclear artillery. (I am confident the author of the blog is knowledgeable about the US arsenal.)
- hga 11y ago
  Fascinating; per Wikipedia, e.g. https://en.wikipedia.org/wiki/W79 https://en.wikipedia.org/wiki/W79 and https://en.wikipedia.org/wiki/W48 https://en.wikipedia.org/wiki/W48 they used a "linear implosion" technique, but it sounds like it had about the same inefficiency as the Little Boy gun assembly design. Which for safety reasons alone are iffy to field, and even more I'd imagine in a quickly accelerated artillery shell....
  - rdl 11y ago
    From reading Command and Control, a lot of the US arsenal was manifestly unsafe for a long time. Based on the number of accidents, and lack of criticality, I suspect there was some super secret design choice or design flaw which meant many classes of weapon would never go critical at all. Someone probably made the decision that only a deterrent was important, so a bunch of unsafe weapons should instead be rendered largely inert while making other gestures of readiness. I don't have any data to support that other than just the lack of unintentional nuclear detonations. http://www.amazon.com/gp/product/B00C5R7F8G/ref=dp-kindle-redirect?ie=UTF8&btkr=1 http://www.amazon.com/gp/product/B00C5R7F8G/ref=dp-kindle-re...
GFK_of_xmaspast 11y ago
Please consider reading about the author: http://blog.nuclearsecrecy.com/about-the-blog/ http://blog.nuclearsecrecy.com/about-the-blog/

vichu 11y ago

This brings to mind the story of John Coster-Mullen - the first person to build an accurate historical replica of Little Boy. I'd recommend reading the New Yorker article on it. It's a pretty fascinating read. http://www.newyorker.com/magazine/2008/12/15/atomic-john http://www.newyorker.com/magazine/2008/12/15/atomic-john