A year ago, China attacked and destroyed an aging weather satellite in orbit. Debris from the Chinese anti-satellite missile test continues to threaten more than 800 operating satellites and will do so for up to 100 years.
At Wired Magazine's Danger Room blog, Noah Shachtman posts a three-part analysis by Geoffrey Forden about the possibility of Chinese anti-satellite capabilities:
Let's start with what we know about China's ASAT capabilities today. And we know quite a bit. Because there are few, if any, secrets in space. Amateurs around the world track most, if not all, of the classified US military satellites from their backyards, posting their positions on the internet. NORAD,is capable of tracking objects as small as four inches across. In fact, NORAD's measurements of the debris caused by China’s January 2007 test were posted on the web. In the case of the Chinese test, the orbital tracks of that debris can be used to reveal the capabilities and limitations of China’s ASAT weapon by reconstructing the collision -- much like forensic scientists reconstruct a crime scene. By backtracking the debris to the point where they all converge, we can determine the two most important aspects of the Chinese ASAT: how China destroyed that satellite, and just how capable its satellite-killer really is.Dr. Forden is optimistic that China would lose a space war with the U.S., at least for the foreseeable future.
The interception was almost head on at a combined speed of almost 18,000 miles per hour. The pieces of debris wound up with the greatest speeds—much higher than the original satellite. This means that China accomplished the most sophisticated of space maneuvers: a hit-to-kill interception, the equivalent of hitting a bullet with a bullet. This is equivalent to what the US is trying to develop in its national missile defense system and is much more sophisticated than the ASAT the Soviet Union was working in the 1980s: little more than a space mine that slowly snuck up on its target and detonated near by.
We also know that the ASAT was highly maneuverable. Yes, the target satellite’s orbit was known well ahead of the interception. However, that does not mean that the satellite’s position was known well enough that the ASAT did not need to steer itself to hit the target. In fact, it is very likely that the interceptor needed to maneuver at high speeds, perhaps as much as six times the acceleration of gravity, to hit its target.
The orbital speed of the target satellite, which is determined by its altitude, also provides us with significant insight into the interceptor’s capability. The closing speed of the interception, which is a combination of the target satellite’s orbital speed and the speed of the interceptor, determines how much time is available to make final adjustments. For instance, just one second before the collision on January 11th, the interceptor and target were five miles apart. During that one second, the interceptor had to make any final adjustments to its trajectory to hit a target smaller than six feet across. Any decrease in the closing speed makes the attack that much easier. Since orbital speeds decrease with increasing altitudes, the Chinese interceptor would find it considerably easier to hit a target in higher orbit.
Finally, the interceptor needed to track its target, so that it could determine where it should move to place itself in front of the obsolete weather satellite; we have a good sense of how that was done, too. The most likely method it employed to track the oncoming satellite was an on-board telescope using visible light. Locking onto a target this way -- as opposed to focusing on the infrared light emitted by the heat of the target, the way the US missile defense interceptor does -- imposes significant limitations on the system. In particular, until it develops a far-infrared capability, which is probably decades away, its ASAT will be forced to attack satellites while they are in bright sunlight.