

Ask HN: What's so difficult about installing a nuclear weapon in a missile? - robomartin

OK. Weird question. I know.&#60;p&#62;Here's the deal: Every so often defense "experts" come on TV news shows to talk about this or that evil power being N years away from having viable nuclear weapons.  One of the arguments I have heard with some frequency goes something like this:&#60;p&#62;"&#60;substitute your favorite evil nation&#62; are at least five years from being able to install a nuclear weapon on one of their long-range missiles.  They may be able to do it in three years on one of their short-to-medium range platforms".&#60;p&#62;OK, well, I don't know the first thing about what it takes to accomplish this kind of thing.  My problem-solver engineering brain goes through a few thoughts, ideas and permutations and I just fail to come-up with a lot of reasons why this one task might be so difficult.&#60;p&#62;I am sure there's someone in the HN community that is an honest-to-Darwin Nuclear Weapons Scientist (or close).  What are the issues with the idea of installing a suitably ruggedized, shock-mounted, thermally-isolated, independently-powered, redundant-microprocessor-controlled, failover-equipped, etc., nuclear power module in a big rocket and lighting 'er up?&#60;p&#62;Don't get me wrong.  I a GLAD that the problem might be difficult.  Whew! The last thing we need is more of the damn things floating around.&#60;p&#62;I just don't understand.
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jug6ernaut
You are over thinking the statement, when they say "install a nuclear warhead
in a missile" they are not speaking to the actual job of installing it. They
use this phrase to represent the finished state of the nuclear device.

The hardest part of developing a nuclear weapon(as i understand, correct if
wrong) is actually getting the fissile material. When experts refer to time
periods(for a nuclear device, not necessarily a full missile) this is usually
what they are referring to. They physics to actually making the nuclear
devices by comparison is much easier to come by.

The process of getting the fissile material usually used is using centrifuges
to separate the heavier u235 isotopes from the other isotopes of uranium. You
can also use a reverse osmosis method to isolate the isotopes but this method
is much more expensive and as such is not usually used by countries trying to
get the first nuclear weapons.

Apart from the nuclear device you also have the construction of the rocket
itself, which is a whole another ordeal itself.

~~~
lutusp
> The hardest part of developing a nuclear weapon(as i understand, correct if
> wrong) is actually getting the fissile material.

No, not for a plutonium-triggered fusion weapon (or a plutonium fission
weapon). Getting some plutonium involves setting up a breeder reactor (as Iran
is now doing). That's hard, but not really hard.

The hard part of a plutonium weapon design is setting it off. Plutonium has a
natural decay rate that's high enough that the core must be assembled very
quickly to avoid a "fizzle", an event where a chance natural disintegration
triggers a non-optimal chain reaction, before the core is fully assembled and
at maximum density.

The single most difficult part of the Manhattan Project was solving this
problem, not acquiring the plutonium used in the devices. The core must be
assembled very, very fast, then an abrupt pulse of neutrons must be generated
at the precise moment of maximum core density.

The Manhattan Project U-235 weapon "Little Boy" was a very simple design that
resembles a gun barrel, because the natural decay rate in U-235 is low enough
that there is little chance of an inadvertent chain reaction. In fact, that
design wasn't even tested in advance -- the prototype was just dropped on
Hiroshima with full expectation that it would work.

The "Fat Man" design was the plutonium device, and the prototype was tested --
on July 16, 1945 -- at great effort and cost, because the team was
sufficiently doubtful that it would work as designed.

During the project, a great deal of effort went into designing lenses of high
explosive, meant to symmetrically compress the plutonium core and assure
correct functioning, but with very, very fast assembly.

So core assembly is by far the most difficult part, and remains so today.

~~~
jug6ernaut
I stand corrected, excellent explanation, thank you.

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speeder
Usually the problem that the newspaper experts are refering is the size of the
bomb.

Making a nuclear bomb that is cumbersome and big is very easy, just put some
plutonium there, and craploads of explosives (ie: "Fat Man" design).

The problem is making a bomb that works, and is small and light enough to fit
a long range missile warhead.

shorter range missiles can be bigger (thus why you can put it more easily on
them).

