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In a typical one hour period, five US low earth orbit satellites pass over the Port of Rajin

Yesterday, I pointed out that the only way for the West to tell the difference between a cargo container full of uranium gas centrifuges and a container full of pig iron as it was being loaded might be increased security associated with the centrifuges. That, of course, assumes two things: 1) that the West can see the loading and 2) North Korea decides that it wants to include the security. After all, Syria apparently decided to do without anti-aircraft batteries and other security measures for its Box on the Euphrates in order to avoid signaling the US that it should pay special attention to that building. We all know how well that worked: it seems to have fooled the US but Israel, with its spies in Syria (the ones who smuggled out the photos of the construction, presumably from a central office in Damascus) managed to obtain the evidence they needed. Unfortunately, it is doubtful that Israel has spies in North Korea (I guess I could be wrong about that) so we are probably left with using technical means to watch the loading and unloading of ships.

One possibility is to use satellites and another is using UAVs. Let’s consider using satellites, mainly because this post is already getting too long. As the image above shows, the US has a great many low earth orbit (LEO) satellites. The orbital elements for these satellites comes from an amateur satellite observers website and could very well include satellites that have ceased to function. (That’s my fault and not the amateur observers. On the hand, North Korea might not know any better than me which satellites were functioning and which are not.) They do not include the Navy’s NOSS satellites which are used to track ship locations. Those satellites were going to be considered tomorrow when I thought we would look at tracking ships on the high seas as a way of determining if their cargo might be suspicious. It turns out, however, that there might be other, more convenient, ways of doing that (See Allen Thomson’s posting and the responses to that) so I’m going to skip that post.

If you simply require that a satellite be above the local horizon to spy on North Korea, then these satellites supply considerable coverage. ( Click here to see a graph of the satellite elevations over the Port of Rajin during a three day period.) Of course, viewing a scene at a grazing angle—unless you are something like an electronics intelligence satellite which could conceivably pick up the radio chatter between security elements—can prove difficult to interpret. Of course, it’s still possible to see things at angles very close to grazing, just things like buildings and trees get in the way. That and the fact that you are looking at very large distances, perhaps as much 3000 km, so the resolution will be very poor.

With that in mind, I plotted the time between satellite passes where a pass is counted as starting when it appears above a certain elevation and ends when it dips below that elevation. ( This plot is shown here for three threshold elevations: 0 degrees, 20 degrees, and 45 degrees.) North Korea, too, could generate just such a plot and know that critical signatures, such as deploying security forces, would have to be timed to fit in between passes. If satellites can detect signatures at grazing angles, then typical separations between US LEO satellite passes is about 10 minutes. That seems very short, though I have no experience deploying security forces. Its worth pointing out that if the satellite is a photoreconnaissance satellite that normally has a resolution of 10 cm at 200 km, it has a resolution of 1.5 m at 3000 km. There might also be a big decrease in sensitivity of electronics intelligence gathering depending on how they normally function.

Going to a 20 degree threshold substantially reduces the slant range but also substantially increases the time between effective passes. Thus, there is an average gap of 34 minutes between satellite passes in that configuration. Much more can happen in 34 minutes than in 10 minutes: more troops could be better deployed etc.

There are still more practical questions to be answered about achieving “reasonable grounds” for interdicting WMD. Clearly human intelligence would be the best. But that has important problems too, such as protecting the life of the informant if you ever have to prove you had “reasonable grounds.” It seems possible to use technical means to increase your confidence by seeing an unusual amount of security. But the most likely clue might simply be the destination: is it another “rogue” nation? Of course, if all the “law abiding” nations won’t trade with a rogue, perhaps their only trade partners are other rogues.