The North Korean Bomb
The New York Times released a good article discussing how this one picture can give you critical details about North Korea’s nuclear weapons program and the internal political posturing of Kim Jong-un. According to an analyst from the Center for Nonproliferation Studies at the Middlebury Institute of International Studies, he estimated the yield at 20 kilotons. This is roughly the size of what they dropped on Nagasaki. Besides the strange looking nozzle at the top, the spherical shape looks like a text book implosion device. This is not the simplest design, but it is much more powerful than than a gun type assembly. An implosion device compresses the plutonium core with simultaneous sublevel explosions from around the edges of the “disco-ball”. The device must be a perfectly engineered sphere, and the detonations must go off in unison or the weapon will fizzle, meaning it won’t get the chain reaction correct, reducing the nuclear yield dramatically. The engineering challenges of this design means this is usually not the choice of a first prototype for an aspiring nuclear power. A “gun type” assembly is usually easier to build, but produces a smaller yield (explosion).
The process of miniaturization for weaponizing these devices, by sticking them on the top of a missile, usually requires more tests, which is why we have been hearing about strange earth quakes in the Northern region of the Hermit nation. So as it stands, it does appear their program is progressing, to the utter dismay of the world. The challenge for North Korea will be to build a lot of them, small enough to be put onto truck launched ICBMs or submarines. Having missiles in stationary silos makes them vulnerable to attack prior to launch. Operationalizing nuclear weapons means being able to retain a credible threat in the face of defensive and offensive measures of their adversaries. Since we are starting to develop some decent missile defense systems, having a lot of ICBMs would increase the chances that some will get through. That takes some work though, so it might be awhile before they get to that point.