Are almost nonexistent: [I]t’s vanishingly unlikely that air
defense systems would be able to even make the shot. The
Chelyabinsk meteor was traveling at something like 32,000 miles
per hour. (A 747′s typical cruising speed? 567 miles per hour.)
By the time you notice it, it’s too late to stop it. Not that
you would notice it. Meteors like the one in Chelyabinsk are
going to pass through the detection systems that humans have.
Telescopes pointed to space are only going to be able to see a
ginormous asteroid. Missile warning and air-defense radars run
via software that ignores things that aren’t planes and
missiles. And the eyes of U.S. military satellites are pointed
the wrong way — down toward Earth. The Defense Support Program
satellite constellation, for instance, is looking for launches
of things like intercontinental ballistic missiles that threaten
America, using infrared. But the asteroid is cold until it
enters the atmosphere. How we could prevent a major asteroid
strike: [W]e don’t have to hit the in