Apparently there is a satellite in free-fall, and we're going to shoot it out of the sky! If you've seen all of the West Wing episodes, you will know that satellites occasionally falling to the earth are not totally uncommon. But this one apparently still has a lot of rocket fuel attached to it, and so posses more of a threat to our lives, etc.
As stated in the NY Times:
Pretty exciting, if you ask me.
The effort will be a real-world test of the nation’s antiballistic missile systems and its antisatellite abilities, even though the Pentagon said it was not using the effort to test its most exotic weapons or send a message to any adversaries.