Leaked documents revealed that the American shoot down of a failed photo satellite in February 2008, was a direct response to the Chinese use of an attack satellite to destroy one of their inoperable weather satellites in January, 2007. The U.S. was alarmed at the Chinese satellite destruction test, and wanted to let the Chinese know that there were American weapons available to do the job quicker and cheaper.
This demonstration took place in early 2008, when a U.S. Navy cruiser used its Aegis radar to locate the target, some 220 kilometers above, before firing a single SM-3 missile to destroy the truck sized satellite. To assist precisely locating the target, larger radars and telescopes were also used. This attack wasn't easy, because the satellite was out of control, and moving erratically. The orbit had to be predicted at least to the point where the Aegis warship could position itself under that orbit. That ability to overcome these difficulties was a good thing. If the Aegis anti-satellite weapon was to be used again, as in wartime, an enemy satellite might try to maneuver to avoid a shot from an Aegis equipped warship.
The 2008 shot took six weeks to plan, mainly because there were so many unknowns. Now, many of those unknowns are knowns and another shoot-down could be carried out much more quickly. How quickly remains a secret. There were other surprises as well. When the 20 pound missile warhead hit the satellite, there was an unexpected explosion, as the hydrazine fuel of the satellite ignited. The flames burned for over twenty seconds. The impact of the warhead (which is inert, just a chunk of metal), was more destructive than anticipated, breaking the satellite up into more, and smaller, pieces. That was good, as those tiny fragments are less likely to hurt anything it hits.
This all began back on January 11th, 2007, when China launched an anti-satellite system (a KillSat, or Killer Satellite) that destroyed an old Chinese weather satellite, about 850 kilometers up. That's at the upper range of where most reconnaissance satellites hang out. The KillSat hit the weather bird, and the result was several million fragments. Most of the pieces are tiny, at least 817 are truly dangerous (at least 10 cm/four inches long, wide or in diameter).
What China did was, in terms of technology, something the U.S. and Russia had demonstrated over three decades ago. No big deal, unless you actually use it. While China has now demonstrated its ability to destroy satellites (at the cost of a launcher and a maneuverable KillSat), it has also caused a major stink among the dozens of nations that own, or use (usually via leasing arrangements) the several hundred satellites in orbit. That's because this Chinese test increased the amount of dangerous space debris by about eight percent. That's a lot. By common agreement, nations that put up satellites, include the capability for the bird, once it has reached the end of its useful life, to slowly move closer to earth, until it burns up as it enters the thicker atmosphere. This approach leaves no debris, which can collide with other satellites, behind. Even a small piece of satellite debris can, when hitting another satellite at high speed, destroy, or fatally damage, it.
A quarter century ago, Russia and the United States agreed to halt such KillSat tests, in order to reduce the amount of "space pollution" that threatened all current, and future space satellites. Moreover, there was the practical problem of cost. Having launchers standing by, to put a sufficient number of KillSats up, would be enormously expensive. And it would simply encourage others to do the same thing, which would cancel the original anti-satellite effort. China has ignored, so far, any criticism of its KillSat test, and dismissed the risk of starting an orbital arms race. But China has angered the other users of orbital space, and earned the contempt of those nations as well. Now we know that it also compelled the United States to test one of its own anti-satellite weapons, and a new one at that.