NAVAL SHIPS MAY SOON lose their sitting-duck vulnerability to missiles. Vessels have little time to defend against the Exocet and other modern missiles that home in on targets at 20 miles a minute and fly low enough to hide in the clutter of radar reflections from waves. But scientists at the Naval Research Laboratory (NRL) in Washington are working on a new radar system that promises to spot such threats faster. It could also improve the radars used for air-traffic control, severe-weather warnings, and pollution monitoring.

The new radar's key component is a so-called agile mirror. Because it's really a reflective sheet of gas molecules, it can reflect 5,000 radar beams every second while pointing each one in a different direction. This would enable radar operators to monitor a 360-degree area while tracking multiple missiles. And unlike current radar systems, agile mirrors could "paint" their targets with beams of different frequencies. "Two frequencies tell you a lot more about the target," says Robert A. Meger, head of NRL's Charged Particle Physics Branch--and would be better at spotting surface-skimming missiles.

A mechanical mirror would be too big to shift position 5,000 times a second. That's why the NRL uses a hot, charged gas, or plasma. The plasma mirror is created by firing a line of electrons through a neutral gas in a box the size of a file cabinet. Meger hopes to have a prototype ready to test by 1998.

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