Late Wednesday night, the U.S.S. Lake Erie used its Aegis missile-defense system to shoot down an ailing reconnaissance satellite as it passed over the Pacific. Aegis is a key piece of the larger U.S. missile-defense system, combining extremely sophisticated ship-borne radars with heat-seeking interceptor missiles that can reach targets in low orbits (such as short- to mid-range ballistic missiles). After successfully using Aegis to knock out a target it was ostensibly never designed for, some may ask if this test of the system proves that the American missile-defense system works.

In a word, the answer is no. The mission is a qualified success for Aegis, since satellites and ballistic missiles share many characteristics at certain stages of flight. But taking out a crippled satellite and destroying an attacking ballistic missile are not the same thing. Most importantly, the satellite's trajectory was known in great detail and it could not maneuver under its own power. That's not the case for enemy ballistic missiles, which have unknown trajectories for large portions of their flights (though we can often guess where they're headed). Advanced missiles, moreover, are likely to be able to maneuver themselves midcourse and release decoys to confuse the missile-defense interceptors. Since shooting a missile out of the sky is a lot like hitting a bullet with another bullet, precise positioning data is crucial.

Finally, Navy personnel were able to choose the location and timing of the intercept. This allowed them to maximize visibility, to wait until the seas were calm enough for an ideal launch, and to keep as many radars and telescopes as necessary nearby to guide the interceptor and track the launch. The satellite was also several times larger than a ballistic missile would have been and was therefore easier to see.

That said, the fact that the Pentagon was able to reprogram missile-defense hardware for an anti-satellite shot in roughly a month is a geopolitically loaded development. China and Russia have long suspected that U.S. missile-defense programs were cover for eventual space warfare capabilities. Indeed, the Pentagon tacitly acknowledged the momentous nature of the mission by giving the secretary of defense final launch authority, rather than the captain of the Lake Erie. Now watch how many other countries suddenly find their satellites are crippled and need to be shot down -- purely for safety reasons, of course.