
Silhouettes of the bomb: what can we learn from the shapes of atomic weapons? - rdl
http://blog.nuclearsecrecy.com/2016/04/22/bomb-silhouettes/
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rdl
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.

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wyager
Source? I'd like to read about this.

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teh_klev
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?

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8note
they should be keeping that secret; good gravity models are a major part of
the difference in accuracy of American missiles vs Russian ones.

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dogma1138
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
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?

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mirimir
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)

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MichaelGG
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?

~~~
Animats
Making a gun-type bomb from enriched uranium isn't that hard. Any shop capable
of building an auto engine could do it. Even machining uranium isn't that
hard; there's a Union Carbide tech note on that. It requires a respirator and
protective gear, but not remote controlled machine tools. That's why anti-
proliferation people are so concerned about enriched uranium.

But enriched uranium is hard to make. The old gaseous diffusion process was
incredibly inefficient - plants over a mile long to make tens of kilograms.
Centrifuges have changed that. Centrifuge plants aren't all that big, about
Wal-Mart sized. They're still expensive. Highly enriched uranium is only made
for bomb purposes; power reactors don't need it (although some submarine
reactors have used it), so it's not made without good reason.

There's some concern about laser enrichment, which apparently works quite well
and is seldom discussed. The US has at least one laser enrichment plant.

Plutonium bombs are hard to get right. A gun bomb with plutonium will pre-
detonate. It takes an implosion. Making a perfectly symmetrical implosion is
hard. The explosive lenses have to be very uniform in density and accurate in
dimension, while being made out of a soft plastic explosive. There are tricks
to the joints where the lenses meet, some of which are still classified. Then
there's the whole detonator thing, although getting the big pulse required is
easier than it was 50 years ago.

Plutonium is a by-product of reactor operation. Thus, there's more of it
around than is really needed. The US and the former USSR made way too much
(tons). But working with plutonium is a huge headache. The dust is radioactive
and poisonous. The PUREX chemical process to refine it from reactor fuel rods
is difficult; places which did it tend to be toxic waste sites now. Its
machining properties are strange; it expands when heated but then doesn't
contract fully. Plutonium bombs usually have a neutron generator to get things
started, and surrounding shells to perform neutron reflection and tamping.
While the general principles are well known, it takes a lot of engineering R&D
to get it working right, including many non-nuclear test explosions.

That's why we don't see terrorist groups making bombs from spent fuel rods.

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caf
Are there _any_ naval reactors that don't use HEU?

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hga
Super carriers have a much bigger space budget than submarines, so I wouldn't
be surprised if they used less enriched uranium. On the other hand, refueling
is a total pain, so that might put a premium on the total U-235 in the fuel
rods (granted, some of the U-238 will breed into plutonium and some of that
will burn up, but...).

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vichu
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)

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sandworm101
"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
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
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
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-
re...](http://www.amazon.com/gp/product/B00C5R7F8G/ref=dp-kindle-
redirect?ie=UTF8&btkr=1)

