Ask HN: What's so difficult about installing a nuclear weapon in a missile? | Hacker News Reader

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

3 pointsrobomartin4 comments

OK. Weird question. I know.<p>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:<p>"<substitute your favorite evil nation> 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".<p>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.<p>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?<p>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.<p>I just don't understand.

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.

> 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.

I stand corrected, excellent explanation, thank you.

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).

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