Monday, September 12, 2016

Will North Korea test again?

Most people seem to think they will. The South Koreans in particular take the view that the site is well prepared (more shafts are available if needed) and so another test is a certainty.

I am less sure. It is likely but there are significant hurdles the North Koreans need to consider. Tests are expensive in terms of fissile material and in terms of international opprobrium. I would say that there are multiple perspectives here that go into the decision to test and Kim Jong Un has the last word - but not the first word.

From Kim Jong Un's perspective - unlike his father or grandfather, he has no comprehension of actual military affairs. He was not brought up in a environment of actual war. So he feels he has to out-do his predecessors and gain the respect of the DPRK military if he is to remain in power. The entire nuclear testing binge is a means to that end.  So unless the tests are visibly productive in the eyes of the DPRK military - it will be difficult for Kim Jong Un to secure their respect by further testing.

From the perspective of the DPRK military - nuclear weapons are a good thing because they make conventional war less likely. The DPRK military really has no interest in actually dying to preserve the Kim mythos. They are happy to fight for their country - but they know exactly how much of the Kim image is pure fiction and I really doubt they want to die to protect it.

That being said - the DPRK military will not know the exact yields of the devices  or the design of the physics package as their own physics people will keep that information compartmentalized. Kim Jong Un will not allow that information to spread. Each and every member of the DPRK military will have to rely on their own personal judgement to determine how effective of a deterrent Kim is really putting together. Here is the real beauty of it - the DPRK military doesn't need to know all the nuclear details because... they will be able to see three things -

1) the international response to the tests, (the international community will tell them what the design most likely is - even if their own scientists (quite rightly) don't do so.)
2) the resources being pulled away from their main operations as the testing and its consequences escalates.(if the tests aren't doing what is expected then more resources will be pulled out of the general reserve and diverted to testing).
3) the South Korean military posture shift.(if the South Koreans are really upset they will put on a major show of force. The details of that show will be sufficient for the DPRK military to determine if the South is deterred from actual conventional action.)

These three things alone will be sufficient for the DPRK military to determine if Kim Jong Un's tests are producing the necessary levels of credible deterrence.

If the tests do not produce the shifts desirable to the DPRK military - it is unlikely that Kim Jong Un will continue testing.

From the perspective of the weapons design team, they are on the hook for demonstrating weapons designs that sit well with existing delivery vehicle payloads. They have a size and weight budget to work to. They also have limited amounts of fissile materials to work with and there is always a supply chain problem. In the initial testing the design team will be keen to see if any yields are demonstrable but as the testing progresses, the team will be under pressure to boost yields without compromising on existing size and weight budgetary targets. 

So far the weapons design team has had some early success. They boosted the yield from 1kT to 10kT. If they want to do something that boosts from 10kT to 100kT *without paying a weight and size penalty* - then that is a tough task. It may be easier to carry out that same increase if they relax the weight and size penalty and just go for broke on everything they can manage design wise to boost by another factor of 10. This means getting some inertial confinement in the "third stage" of the device. Again - sounds good in theory - but if they have to test a device - they have to make sure the test site is suitable.

One of the lesser known aspects of developing multistage devices is that it is difficult to exactly predict the coupling between stages. This manifests as fizzles and devices exceeding predicted yield. Now it your estimate of 100kT exceeds by a factor of 3 - then the site might not be able to handle it and you will likely kill your own team. That will keep passions for higher yields to a manageable level (A fact that I feel has restrained India's exploration to a greater degree than most recognize).

From the perspective of the delivery vehicle team, they have to prove that they can inject the BM into a well defined trajectory. This is quite hard for anyone who doesn't have gyros and gradiometers of the right kind. The problem is quite a bit harder when you launch out of the sea. Unless the delivery vehicle team shows the ability to produce a repeatable injection with say 10-ish launches. There is really no sense in having the weapons design team proceed with a design that exceeds current payload budgets.

So this idea of another North Korean nuclear test is far from clear cut.

I am sure that many North Koreans would like more tests but the material reality may be quite distinct from what most of them recognize.


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