Science: Newest Nuclear Tests: What They Hope to Prove

Atomic Energy Commission scientists last week were "keyed up and ready" to take the U.S. into a new high level of nuclear testing. First shot on the agenda: a giant skyrocket exploding not more than 60 miles above Johnston Island, its sub-megaton flash visible in Hawaii 700 miles away, its power sending waves of electrical disturbance around the earth to be picked up by sensitive instruments.

Later shots in this latest series of U.S. nuclear tests will carry a bigger bang and go off far higher above the surface of the earth. If not obscured by clouds, these explosions will be seen in Hawaii as brilliant flashes of light in the night sky, probably followed by enormous and rapidly swelling fireballs. They will dazzle the naked eye like glimpses of the sun, doing no permanent damage; but the AEC warns that it will be extremely dangerous to look at the lofty explosions with binoculars or telescopes. Concentrated on the eye's retina, the light will be strong enough to cook a fair-sized blind spot.

Smoke Screen. Purpose of the high-altitude shots is both military and scientific. Nuclear explosions in the vacuum of space or in the thin fringe of the atmosphere do not behave as they do in the dense air near sea level. Little or none of their energy goes into shock waves; most of it escapes as X rays, neutrons, and other varieties of radiation that are relatively unimportant in ground-level bursts. But military men are most anxious to learn what this radiation will do to missiles and satellites, and even to aircraft.

The tests will also demonstrate the electrical effects of high-altitude blasts. When a nuclear weapon explodes in the thin air more than ten miles above the earth, it creates vast numbers of long-lasting free electrons. If they are numerous enough, the electrons can absorb and reflect many kinds of radio waves. The AEC estimates that a one-megaton weapon bursting at a 50-mile altitude will disrupt high-frequency radio waves (the most useful kind for long-distance communication) for 600 miles around.

The most serious military effect probably concerns radar—particularly the powerful radars that are being developed to spot ballistic missiles plunging down from space. A high-altitude nuclear explosion, the AEC explains, acts like an enormous, radar-blinding smoke screen. Radar beams that search the sky for invading warheads may be either absorbed or totally reflected by bomb-ionized air. An enemy hoping to hit a target defended by radar-guided anti-missile missiles might well explode a warhead several hundred miles up to create an electronic smoke screen that would blind defensive radars to other warheads racing toward their targets.