Recent news reports of a third underground nuclear test in North Korea have quickly faded from the news. Digging behind the scenes, I see some indications our intelligence community is trying to find out whether it was a plutonium or uranium bomb.
Last December, the North Koreans launched a satellite into orbit more-or-less successfully (see the earlier article dated 12-13-12 and titled “On the 12-12-12 North Korean Satellite Launch”, and also the article dated 4-6-09 and titled “Thoughts on the North Korean Rocket Test and Beyond”). While the satellite itself was apparently dead-on-arrival, the rocket worked just fine, for the first time.
In principle, any satellite launcher is also an intercontinental ballistic missile, the only difference being the details of the flight path one commands. The range as a missile just gets shorter as the payload gets heavier.
That satellite (around 220 pounds) was far smaller than a first generation (crude) nuclear weapon (around 9-10,000 pounds). A second or third generation weapon would be far smaller, and would fit that rocket much better. See also the article dated 3-10-12 and titled “On Iran and the Bomb”.
A while back, I ran some crude calculations with the scarce and contradictory information available about their rocket, the Unha-3 (that’s the 12-13-12 article). These numbers indicated that their rocket might reach the continental US, if they can get their bomb down to around 2000 pounds or less.
That would still be a fairly low-yield weapon: several tens of kilotons, perhaps. It will take them only a few years of bomb test work to do that, same as it took for us long ago. You can bet that they have very bright people working on it.
There’s more to a real ballistic missile system than just the rocket and a bomb that fits it. Hitting cities requires very precision guidance (that the “any orbit will do”-satellite doesn’t really need). The bomb must survive hypersonic atmospheric reentry , which means it has to fly stably at such speeds, and it must have a heat shield.
There’s no evidence that they have any of these other things yet, so the smaller, lighter bomb may not be the pacing item for a North Korean “city-busting” capability against the US. But, is that the only mission they might want to do?
Consider a different way of damaging the US (or anybody else), not by the blast and fire, but by the electromagnetic pulse (EMP) of a very high-altitude detonation. Even with a small bomb, this is known to destroy electronics, and damage the electricity grid, over a very wide area, far larger than any city.
We first seriously encountered this effect from the July 1962 “Starfish Prime” test above Johnston Island in the Pacific. That warhead was about 1.4 megatons, detonated about 250 miles up. Quoting from the 2-14-13 version of the Wikipedia article on this test:
Starfish Prime caused an electromagnetic pulse (EMP) which was far larger than expected, so much larger that it drove much of the instrumentation off scale, causing great difficulty in getting accurate measurements. The Starfish Prime electromagnetic pulse also made those effects known to the public by causing electrical damage in Hawaii, about 1,445 kilometres (898 mi) away from the detonation point, knocking out about 300 streetlights, setting off numerous burglar alarms and damaging a telephone company microwave link. The EMP damage to the microwave link shut down telephone calls from Kauai to the other Hawaiian islands.
For an EMP mission, there is no need for a stable reentry vehicle with heat shield, or precision guidance. The blast point is at, or above, the very edge of the atmosphere. All they need is the rocket, and the smaller bomb to fit it, and the effect is so widespread no precision guidance is needed.
A rocket and a bomb to fit it are exactly what the North Koreans have been working on!
The same is true of Iran! They have not yet tested a bomb, but they have launched two satellites, and they are known to be enriching uranium with centrifuges.
Does plutonium versus uranium make a difference? Maybe.
It is easier to build lighter and more compact weapons with plutonium, once you have mastered the difficult triggering technique. The plutonium is bred from natural uranium in a nuclear reactor, so you need some of those in operation, and they are easy to spot.
The trigger technique is much easier for the slightly larger and heavier uranium bomb. For enriched uranium, you do not need a reactor. The key to that process is the gas centrifuges, which are easy to hide. That, too, is what Iran is doing, and if the North Koreans are also doing it, we have not spotted it.
If I had to guess, I’d say the Iranians are headed for a uranium EMP weapon to ride their rocket, which they intend to reach Europe, as well as Israel and their other neighbors. They just haven’t reached the warhead test stage yet, nor have they begun figuring out how to make it lighter to fit their rocket. With the somewhat shorter range requirement as compared to North Korea, their bomb need not be quite as light, anyway.
Also my guess: the North Koreans are headed for a plutonium EMP weapon to ride their rocket that must cross the Pacific. They’ve begun warhead testing already, and will soon figure out how to make the lighter version to fit their rocket: which just successfully flew for the first time last December.
For both North Korea and Iran, their nuclear weapons will be able to do more damage as EMP weapons than as direct blast and fire weapons. That choice eliminates the need for stable entry vehicles and heat shield designs, and the precision guidance.
Just shrink the bombs, and they are ready to hurt other folks very badly.
And it’s only a small handful of years off ……