Policing the Big Beat

Scientists studying the provisions of the nuclear test ban treaty have voiced few fears about their ability to detect most violations--either under water or in the atmosphere. But what about the farther reaches of space? On that problem, even wishful thinkers have their doubts. "What if the Russians run a clandestine test behind the moon?" they ask. "Or do it forty million miles away from the earth?"

These are not idle fears, but U.S. nuclear authorities have not been idle about them either. For five years the Atomic Energy Commission has anxiously been pushing a project code-named Vela-Hotel, designed to detect nuclear explosions in space. Last week the Hotelmen delivered their first package of special instruments. Before the end of 1963, similar instrument packages are scheduled to take the long rocket-ride into space on Air Force-launched satellites.

Cleanest Lab. Though test explosions in distant space would be both difficult and expensive, scientists say they have extremely important advantages. "Outer space," says Dr. Richard F. Taschek, head of Los Alamos' Physics Division, "is probably the cleanest possible laboratory for testing bombs." There is no matter around to falsify results, and all effects of an explosion can be measured with great uniformity.

One simple way to perform such a test would be to launch two spacecraft at about the same time. One would carry the bomb; the other would be loaded with instruments and radio equipment.

When they reached the desired positions, perhaps one million miles from the earth and a few hundred miles apart, a coded signal from the earth could explode the bomb, and the "diagnostic" spacecraft would report by radio just what happened.

But if diagnostic craft can be sent aloft for a test, they can also be orbited to watch for tests. At present, they are the only practical policemen U.S. science can build. When a nuclear bomb explodes in the vacuum of space, it does not give the great flash of light that it gives in the atmosphere. About two-thirds of its total energy appears as a brief, enormously powerful burst of soft X rays, rather like those that are used to treat skin diseases. Those soft X rays cause a soft glow when they hit the atmosphere, but they are dissipated long before they reach the earth. There are also small amounts of gamma rays. Like the X rays, these are electromagnetic radiation that travel with the speed of light (186,000 miles per sec.). Following behind at less than one-tenth the speed of light come neutrons from the nuclear reaction. Most of the rest of the energy released goes into the vaporized debris of the bomb and its casing, which expands into space at less than 200 miles per sec.

Delayed Debris. Easiest to detect--provided the proper instruments are orbiting in space--are the soft X rays; they are by far the largest product of the explosion. The Vela-Hotel instrument package is expected to detect soft X rays from a one megaton explosion 200 million miles away from the earth and distinguish them from X rays from solar flares and other natural sources. Some instruments are also sensitive to gamma rays and neutrons.

It might be possible to conceal a space test by means of a large amount of lead dust dispersed in space between the test and the earth, but this maneuver would be extremely expensive and far from dependable. Tests done behind the moon would not be dependably secret either; they would be revealed by delayed gamma rays from radioactive debris spreading from behind the moon's small shelter. A test on the far side of the sun might possibly escape notice for a while, but its cost, the time it would take to get in place, and its undependability would make it hardly worthwhile.

Suspicious Sniffers. If no special instruments are watching, cheap clandestine tests not far from earth could present a considerable temptation; but the U.S. intends to get detection apparatus working in space as soon as possible. Present plans call for two satellites launched by the same rocket. They will climb to 60,000 miles, well above the influence of the earth's magnetic field. There they will separate and be jockeyed into positions about 180 miles apart on the same orbit. They will circle the earth once every 92 hours, sniffing for suspicious bursts of soft X rays. Soon other satellites will join them. If any nation breaks the test ban, the same apparatus will be ready for taking part in immediate U.S. space tests and reporting the results.

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