For Clementine Scientists, Small Is Beautiful

THANKS to the ``Star Wars'' antimissile program, planetary scientists should soon have a detailed geological map of the moon and a close look at one of the Apollo asteroids. Those are the kind of asteroids that might one day slam into Earth.

The mission is called Clementine. Its launch window opens Jan. 25 at Vandenberg Air Force Base in California. This mission sets important precedents for both the United States Department of Defense (DOD) and the National Aeronautics and Space Administration (NASA). It combines civilian scientific exploration with tests of military hardware. What's more important, this is the first example of the kind of cheaper, quicker, high payoff missions that both agencies want to emphasize in the 21st century. Simple and quickly deployed

Instead of relying on a few complex and costly ``spy'' satellites, the DOD wants cheaper, simpler satellites that can be mass produced and quickly deployed in low orbits. For his part, NASA administrator Daniel Goldin wants to emphasize scientific missions that also are relatively cheap and quick to execute. He talks of costs under $100 million (rather than over a billion dollars) per mission and time scales of a few years from initial mission approval to beginning operations.

Clementine meets these objectives. It is coming in at a little less than $100 million for a mission spacecraft and a spare. January's launch, if successful, will come 22 months after NASA and the DOD told the Naval Research Laboratory in Washington to proceed with development.

The craft will test a variety of lightweight sensors using natural targets under deep-space conditions. It will stretch the capability of a new high-power, lightweight computer during months of autonomous navigation. But, while they are relatively cheap and lightweight, these sensors can scan objects across a wide range of infrared, visible, and ultraviolet wavelengths. They can characterize objects like the moon and an asteroid in detail. The computer that manages them and the spacecraft has something like a third of the power of a major supercomputer. All of this capability is packed into a spacecraft that weighs only about 500 pounds without its fuel.

This powerful surveillance package is designed primarily to meet the needs of the Ballistic Missile Defense Organization. However, given the opportunity to test it on the moon and an asteroid, United States Geological Survey geologist Eugene Shoemaker says it ``is an excellent science mission and the team is pretty excited.'' Benefits from mission

Dr. Shoemaker, who heads the mission science team, says Clementine should be able to map the entire moon in terms of rock type. It should typically show details as small as 150 meters (500 feet) across. Then, in May, it will go on to fly within 100 kilometers (60 miles) of the asteroid Geographos next August when the asteroid is about 3 million miles from Earth.

This is an Earth-crossing asteroid. That means that its orbit intersects that of Earth. As seen from Earth, Geographos appears to be an elongated object about 3 to 4 kilometers wide by 1.5 kilometers long. But Shoemaker says that ``it's a real mystery as to what this object really is.'' He says it could be two objects gravitationally linked together. They may even be touching. The Clementine instruments should show the craters, cracks, and loose ``soil'' on Geographos.

Asked if Geographos might some day hit Earth, Shoemaker said there is about a 30 percent probability of an impact sometime during the next few million years.