Word: beams
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...easiest to find: the intense heat of a missile's rocket thrusters, concedes the anti-S.D.I. Union of Concerned Scientists, makes it stand out "like a firefly in a darkened room." That is also when a missile defense is most efficient: a single hit, by a laser beam, for instance, can destroy ten warheads at once. In post-boost and mid-course phases, the separated warheads are vastly more difficult to find and distinguish from decoys. On re-entry, the decoys burn up, and only the warheads continue to plunge through the atmosphere. But if there...
Chemical lasers, utilizing the reaction of gases such as hydrogen and fluorine, are the most powerful lasers now in use. But a missile-killing laser beam might have to be 10 million times as powerful as the one that the Air Force is now using in antisatellite weapons tests. Also, because its long wavelength somewhat spreads out its focus, a chemical laser beam might have to be held on precisely the same spot on a missile's skin for as long as seven seconds; during that time the missile might rise 20 miles. Because a ground- based laser could...
Excimer lasers, which use a different kind of chemical reaction, produce beams of short wavelengths that could destroy a missile by focusing on it for only a second or so. But the generating apparatus is so bulky that it could not be lifted into orbit; the laser stations would have to be placed on mountaintops to put them above the densest layers of the atmosphere. Even the thin upper layers would cause the beams to shimmer, however, owing to the same phenomenon that makes the light from stars appear to twinkle. The excimer laser beams would have to be bounced...
This much is known: a part of the enormous energy released by a nuclear explosion can be converted to powerful X rays by rods projecting from an atomic device in the microsecond or so before the rods themselves are vaporized. The beams are so powerful that they need no "dwell time" at all; they could knock out a missile or warhead instantaneously. Less precision is necessary in aiming them; an X-ray laser "beam" as wide as two football fields would have great destructive power...
...type of charged-particle beam, the electron beam, can operate in the atmosphere, though currently only over very short ranges. Livermore Laboratory has been working on and off since 1958 to develop an electron beam for terminal-phase interception. The current idea is to station a sort of gun on the ground near a group of missile silos or a city and fire electron beams at incoming "physics packages" (a remarkably polite euphemism for atomic warheads) as they re-enter the atmosphere. The beams, however, are hard to aim and control. Not to mention the price tag: Researcher Bill Barletta...