Geoff FordenChinese BMD Test: Illuminated by the Sun?

click on the image for a larger version

These two views show a target warhead 350 km directly above the Jiuquan Satellite Launch Center at 7:45 pm (local time) on 11 January 2010. The image on the left shows what the target warhead (with an altitude of 350 km) would see if it looks at the Sun and the right shows the geometry of the Sun, Earth, and target warhead at at that instant.

I am starting to conclude that the “eyewitness” to the Chinese missile defense test is probably real, the reported time (7:45 pm, “local time”) is reasonable, and the target vehicle was most likely a relatively short range missile such as the DF-21. The slower the target vehicle, the more reasonable the streak seen on the camera phone’s image becomes. One very important question can still be addressed: was the target illuminated by the Sun? The answer to this question is vastly important. If the target could not be illuminated by the sun, it would mean that the Chinese have developed much more sophisticated infrared sensors than they have flown previously. If, on the other hand, it could be illuminated by the sun, perhaps by selecting an intercept point high enough for the sun to illuminate the target, then we are not forced to conclude a dramatic improvement in IR technology.

7:45 pm sounds pretty late at night. (Especially during the winter!) However, we must not forget that China is a very large country that uses a single time zone. That means that when it is 7:45 pm in Beijing, it is also 7:45 pm local time at the Jiuquan Satellite Launch Center almost 1,400 km west. On 11 January 2010, that corresponded to11:45 UTC. How high up would the target have to be to still be illuminated by the Sun?

At that time, the Sun was 17.4 degrees below the horizon at Jiuquan SLC. It’s a simple exercise in geometry to show that an object needs to be at an altitude of 305 km or greater if it is to be illuminated by the Sun. That is easily achievable by a DF-21 flying a maximum range trajectory.

I suppose that some people will still want to believe that China has achieved a quantum leap in IR technology. I cannot prove them wrong. However, I believe that such improvements come in systematic ways; especially if the developing country wants to master the technology for the long term. This test is still consistent with the Chinese hit-to-kill technology using a visible light tracker.


  1. 3.1415 (History)

    If the hit depends on optical rather than IR sensing, is 11:45UTC the optimal time to do this? Would doing it during daytime better than doing it at early evening?

  2. Geoff Forden (History)

    Approximate Pi,

    No, there are circumstances that would make early evening far preferable for testing a BMD system using a visible light sensor than in broad daylight. I plan on going into this in more detail in a future post but consider the geometry where both the target and the interceptor are both in the downward portions of their trajectories. (This is, in fact, the case for US missile defense test in order to minimize the production of space debris.) In that case, it is likely any view that included the target would also include part of the Earth’s surface. If that, too, was illuminated, it would make target acquisition considerably harder. So timing the intercept so that the target was illuminated but the Earth was not is highly desirable.

  3. 3.1415 (History)

    What’s so special about IR sensing? Can’t one use ground-based laser to keep the target painted, since it can be tracked?

  4. Anon.

    Approximate Pi’s thought interestingly links in with this

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