Science: Hypermissile

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The long-range, thermonuclear ballistic missile is an "ultimate" weapon in only one sense: defense against it is so difficult that it may prove impossible. But if adequate defense is ever achieved, missiles can learn new tricks and become "ultimate" again.

This month's Jet Propulsion is devoted to hypervelocity flight—the perilous maneuvers of futuristic vehicles flying at 10,000 m.p.h. and more in the thin, high fringe of the atmosphere. In the eyes of out-front rocket men, the ballistic missiles that dominate today's military dreams are pretty crude jobs, outmoded even before they are built. Since they follow elliptical courses through space, they must climb more than 1,000 miles to reach a respectable horizontal range. The climb costs vast amounts of fuel, making the missiles expensive and unwieldy. The curve of re-entry is simple and predictable. If the missile's motion is plotted by the enemy during any part of its flight, its full trajectory can be computed. Then perhaps a defending rocket can be shot up from the ground to meet and destroy it.

The danger of such confrontation can be reduced by evasive maneuvers at hypervelocity. Instead of bulling its way to its target like a crude ICBM, a hyperspeed missile will either skip or glide. If it skips, it will climb into space about half as high as a ballistic missile of the same range. Instead of plunging down to earth, it will skip off the top of the atmosphere like a flat stone off the surface of a pond. By doing this several times, if necessary, it can reach a distant target over an unpredictable course. The glide missile is simpler. It merely climbs up 50 miles or more by rocket power, turns horizontal and glides to its destination at something like 10,000 m.p.h.

Red-Hot Heat. Both skip and glide have their partisans. Dr. A. J. Eggers Jr. of the National Advisory Committee for Aeronautics is a glide man. He figures that both skip and glide missiles are more efficient load-carriers for long ranges than ballistic missiles are. but he thinks that skip missiles will get too much heating and jolting during their violent acrobatics. Glide missiles will have to contend with heat only, and he thinks they can take it. When they speed through the high atmosphere toward a target 5,000 miles away, the temperature of their skin may reach about 1,600° F. This is a bright red-hot, but Eggers seems to think that proper material and careful design can bring the missile safely through its ordeal of fire.

A glide missile, Eggers says, should be shaped rather like a child's paper dart (see cut). The slim conical body should have a blunt point, which does not get as hot at hypervelocity as a sharp point does. The leading edges of the wings and fins should be blunt too. This shape should radiate away enough frictional heat to keep the temperature of its skin below the softening point.