Exploring the High-Tech Frontier

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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 not send a beam around the curve of the earth, the generating apparatus would have to be carried aboard a fleet of satellites in low orbits. How many satellites would have to be sent aloft in order to keep some in range of Soviet missile-launching sites at all times is a subject of fierce debate among scientists; estimates have ranged from 100 to 1,600, which again means nobody really knows. In any case, the satellites would be monsters, each weighing 100 tons or more.

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 off mirrors in very high geosynchronous orbits over the equator, meaning that the mirrors would always hover over one spot on the earth's surface, to give the mountaintop stations a constant target to aim at. The geosynchronous mirrors would detwinkle the beam and reflect it to "battle" mirrors in low earth orbit. The battle mirrors would aim the laser beam at missiles or warheads. The mirrors would have to be gigantic, as much as 90 feet in diameter for the geosynchronous variety, and of almost unimaginable perfection; the slightest pitting or warping could cause a laser beam to scatter. Chemical lasers would need aiming mirrors (diameter: 30 ft.) atop their satellites too, and those mirrors would also have to be just about perfect. Star Wars Supporter Edward Teller considers fleets of laser satellites and orbiting mirrors too expensive to make chemical or excimer lasers practicable for missile defense.

That leaves X-ray lasers, which are being investigated under tight secrecy at the Livermore Laboratory. Grumbles Teller: "Methods that have real expectations of success are classified, and methods that have little possibility of success are advertised."

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.