Golf Ball in the Sky

Perched in the nose of a Delta rocket, one of the simplest satellites ever built by the U.S. roared off the launch pad at Vandenberg Air Force Base last week to begin an 8 million-year journey in space. The 2-ft. sphere, placed into a 3,600-mile-high circular orbit, contains no moving parts or electronic equipment and resembles an oversized golf ball. Yet it should provide earthbound geophysicists with a benchmark in the sky that will enable them to measure precisely the rotation rate of the earth and the wobble of its axis, continental drift, and the movement along geologic faults. It may even supplement the developing technique of earthquake prediction.

Dubbed LAGEOS, for laser geody-namic satellite, the new satellite consists of an aluminum shell dimpled with 426 so-called cube-corner prism reflectors. Each of the prisms reflects directly to the source a laser beam striking it from any angle. Inside the sphere is a solid brass core, which contributes most of the 903-Ib. satellite's weight. Because it is so small yet has so much mass, LAGEOS will not be much affected by any traces of the earth's atmosphere, particles in the solar wind, or variations in the earth's gravity field. As a result, its orbit will be extremely stable, and its position at any time can be precisely determined.

Future Map. NASA, working through the Smithsonian Astrophysical Observatory, will aim high-powered pulses of laser light at the satellite from positions on the earth. By measuring the length of time the light needs to travel to the satellite and reflect to the laser stations, scientists will be able to calculate the exact distance from each laser gun to LAGEOS. Thus, by placing stations on each of the dozen or so tectonic plates that constitute the earth's surface, they can track the rate and direction of the plate movement, which results in continental drift. With stations on each side of the San Andreas fault, geophysicists will be able to calculate the exact movement along the great crack in the earth's surface, which could aid in forecasting California's earthquakes.

NASA scientists estimate that measurements made during the first four years of the program should be accurate to within four inches. But eventually, once the measurement techniques are perfected and more laser stations become operational, movements of the earth's surface as small as .4 in. per year, averaged over four years, will be detected.

Because LAGEOS is expected to remain in orbit for so long, NASA has placed aboard it two stainless-steel sheets, each etched with a message conceived by Astrophysicist Carl Sagan of Cornell University. Designed to inform extraterrestrial visitors or future inhabitants of the earth about the LAGEOS mission, the message shows three maps of the earth, depicting the continental drift that the satellite will help observe. The uppermost of the maps shows the continents as they are thought to have existed 225 million years ago, when Africa and South America were joined. The middle map is a picture of the planet as it exists today and indicates the satellite's launch site in California. The lowest map portrays the earth as scientists assume it will look some 8 million years from now; it shows Australia welded tightly to the East Indies, and East Africa separated from the rest of the continent.

This map also predicts California's future. The sliver of the state west of the San Andreas fault, including Los Angeles, has split from the U.S. mainland and is heading out to sea.

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