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Sorry if this question is inappropriate for this SE or perhaps too technical but it is frankly a genuine concern for me.

Basically, the question is, how much should the claims of NK be believed? My specific reasons for skepticism are:

  1. Hans Bethe, a very great physicist who was key to the Manhattan Project, mentioned the need to machine plutonium as being a reason that non-state organizations like terrorists would have great difficulty making an a-bomb and I would guess other aspects like the initiator are non-trivial. Uranium gun-type bombs are problematic as I understand it for other reasons, probably isotope separation. Now, NK is a state of course but it lacks resources that other countries possess.

  2. The range 15K kilometers which I believe make every site in the world a potential target, but is not such a range unlikely? I do not fully understand ballistic missiles: can such a missile accurately reach targets from its initial thrust alone or are in-flight corrections needed and also I think the missile has to know when it is near the target. How is navigation accomplished? I assume the GPS system can selectively deny info to anyone we choose.

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    GPS is not the only navigation system. Russia and China have theirs too
    – whoisit
    Sep 18 at 3:25
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    GPS arrived significantly after the first ICBMs. Accuracy with nukes is only really necessary against hardened military targets like bunkers or ICBM launch pads. 1960s tech made it work, 2020s certainly can, provided the enrichment hurdle is passed. What might be holding NK back is warhead miniaturization: you can't put a WW2-sized A-bomb on a rocket. In short: NK's bragging is hardly to be trusted, but it would also be foolish to think they will never surmount the difficulties and they've tested both bombs and missiles, only separately to date.
    – Italian Philosophers 4 Monica
    Sep 18 at 3:28
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    @ItalianPhilosophers4Monica It is interesting to think about tech from those days -- we all know about computer memory but what amazed me, never in a million yrs suspected is that satellites sent photos via metal cannisters -- no way to transmit photos electronically, at least not with the avail tech. Cannisters simply dropped from orbit with I guess a parachute.
    – releseabe
    Sep 18 at 3:36
  • @ItalianPhilosophers4Monica: I am guessing that they use gun design and implosion might indeed be something they are not currently able to produce -- what do u think?
    – releseabe
    Sep 18 at 3:38
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    No, ICBM tech is basically launching something into a trajectory that is almost, but not quite, an orbit. Orbiting nuclear weapon systems are banned from space, but if you think about it, your X, in the case of a satellite, would be infinite. That's not to say that 15k isn't quite a bit harder than 5k, it's just not as hard as one might think.
    – Italian Philosophers 4 Monica
    Sep 18 at 4:33

1 Answer 1

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  1. The Manhattan Project was started with 1940s-era technology. Back then, it pushed the state of the art. 80 years have passed since then. The function of an implosion bomb depends on precision machining of the plutonium pit and the surrounding explosives and on the precise timing of the trigger. While some technologies involved in this are still on various export control lists, this will merely slow a state-level actor, not stop it.
    Unless there was an incredible bluff with lots of buried conventional explosives (and people looking at seismic waves think it was no bluff), we do know that North Korea can trigger a nuclear explosion in an underground cave. That does not mean they can put their device on top of a missile, but it would be risky to think they cannot.
  2. ICBM were build with 1960s-era technology. Back then, they pushed the state of the art, literally rocket science. 60 years have passed since then. Again, there are export controls on some of the involved technologies.
    Here we know slightly more; an ICBM can be launched on a trajectory which is optimized for range or on a trajectory which is optimized for height. The North Koreans test on a height-optimized trajectory and people can do the math which range that gives. What is unknown is how much payload those test shots carried.
    Here is a 38north analysis of recent tests. Note that they are very much an anti-DPRK site.
  3. Weapons analysts talk about the circular error probable to measure weapon accuracy. CEP is the radius of the circle which holds, on average, 50% of the shots fired.
    When smart bombs are dropped on bridge spans on individual vehicles, a CEP of a few meters is required. Using nuclear weapons against hardened targets like a missile silo requires a CEP of tens or hundreds of meters. This is called counterforce targeting. Using nuclear weapons against soft targets like a city requires a CEP of several kilometers, especially with megaton-range warheads. This is called countervalue targeting.
    Back during the Cold War, the UK had the so-called Moscow Criterion -- the Soviets could obliterate the UK, the UK could obliterate a few Soviet cities, which should give any rational Soviet leader pause.
  4. GPS can be selectively degraded by switching to an encrypted mode. That would immediately cripple many GPS-enabled services in modern industry and commerce. In addition to GPS (US), there are BeiDou (China), Galileo (EU), and Glonass (Russia). Pulling the plug on all of them on short notice would be a challenge.
    Imagine North Korea does another test and for one hour, car navigation systems all over the West Coast misplace the positions by a mile.

North Korea has not properly tested their ICBM. It has not flight-tested their warheads (other nuclear powers haven't done so for a very long time, either). Combined, this gives a big question mark on the reliability and accuracy of their arsenal. But how many US cities is the US President going to bet on this assessment? How many South Korean or Japanese cities?

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    +1. 2 things: Modern ICBMs seem to be mostly H-bomb based, which may make high yield warheads lighter. NK has only tested A-bombs, not H-bombs. Second, that high-altitude trajectory may be a way to simulate its distance capability without having to send it too far afield (howitzers fire furthest at 45°, but 60 and 30 may yield similar ranges). At some point, testing a 15k missile to 15k looks like a live shot...
    – Italian Philosophers 4 Monica
    Sep 18 at 6:15
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    @ItalianPhilosophers4Monica To my knowledge the only way to detonate an H-bomb is to use an A-bomb as the detonator. So I don't think an H-bomb is any lighter and it is definitively technically a lot more complicated.
    – quarague
    Sep 18 at 6:20
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    "Close enough" counts in horseshoes and nuclear weapons. A ten kilometer CEP is "close enough" to still kill lots of women & children and to still cause lots of general chaos. A 10 km CEP doesn't require any post-launch corrections. Look at what India has just accomplished: They have landed a vehicle on the Moon, with high precision. No country is sharing its classified technology with India. India did this all on its own but with lots of help from openly available information. ICBMs are easy compared to a Moon landing.
    – David Hammen
    Sep 18 at 9:48
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    @quarague lighter relative to the explosive force that is. You only need a minimally sized a-bomb to trigger the fusion
    – Hobbamok
    Sep 18 at 14:38
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    @paulj, tons of drugs and many people are caught. And the weapons would have to be prepositioned. Do you think a society like the DPRK would trust a couple of covert operators in a foreign land, a Western land, to guard their retaliation capability?
    – o.m.
    Sep 18 at 16:06

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