Satellites on Patrol

If the Russians plan to try clandestine nuclear tests deep in space, they now have less chance than ever of getting away with it. Last week the U.S. orbited two vigilant satellites loaded with sensitive instruments capable of measuring X rays, gamma rays and neutrons from any source and any direction. Taking positions 65,000 miles up and on opposite sides of the earth, they joined a similar pair that was launched last October and has been performing far better than its builders had hoped.

The Department of Defense, which ordered the satellites from Space Technology Laboratories, and the Atomic Energy Commission, which supplied their instruments, insist that they are only innocent research devices aimed at learning how to detect atom tests in space. They are, in fact, a nuclear testing control system already in successful operation. The satellites launched last fall have been working perfectly three months longer than their expected life; their builders think they will stay on the job for at least nine months more without giving trouble. The two that were fired aloft last week should have an even longer life, and they carry more and better instruments.

Dr. Robert Frosch, director of the Pentagon's Advanced Research Projects Agency, is sure by now that the present level of solar activity cannot confuse even the earlier satellites into giving a false alarm. But this is the sun's periodic quiet period; when it goes back into its active condition in a few years, blossoms with sunspots and flares and bombards the earth with streams of high-energy particles, the satellites may send in some puzzling reports. "There are still a number of ambiguities that we know nothing about," says Frosch.

Those first satellites, which orbit high above the normal Van Allen radiation belt, says Dr. James J. Coon of the AEC's Los Alamos Scientific Laboratory, have detected peculiar cone-shaped clouds of negatively charged particles, presumably electrons, that trail the earth to an unknown distance, circling at the same speed with which the earth turns, so that they always remain on the side away from the sun. No one knows where they come from or why they follow the earth. Instruments on the newer satellites are designed to find out more about them.

Both the Pentagon and the AEC are sure that no nuclear test has been exploded in space since the first detector satellites were tossed into orbit. Their instruments would have detected even a small (20 kilotons) explosion 100 million miles away and distinguished its effects from all kinds of natural radiation. This is believed to be a modest estimate of their capabilities. "How much better we can do now," said an AEC official, "we're not telling."

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