Current missile defenses consist of missiles fired at other missiles. If Lockheed Martin has its way, that may change in a few years, with missiles being shot down by laser beams.
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Lockheed's system is called Area Defense Anti-Munitions, or ADAM. It's a 10-kilowatt laser that can be fired at a target up to 1.2 miles away, and ADAM can track missiles at up to 3 miles away. It's designed for battlefield use against improvised rockets fired by ground troops or insurgents, so it's more akin to Israel's Iron Dome rather than the Patriot and THAAD antimissile systems, designed to track and destroy weapons operating hundreds of miles away.
The advantage of laser-based defense over missile-based is that tracking is less complex. Missiles need to calculate trajectories and even be able to maneuver (as with Iron Dome) toward their target. Lasers do not. Plus, a laser beam moves at the speed of light, so at a range of a mile, it can hit its target in less than five-millionths of a second. Lastly, laser weapons cost less to fire, since they aren't using up real ammunition, jut power.