Ask A Satellite For Directions

No well-prepared Boy Scout troop would wander into the wilderness without a compass. But Scouts may soon have a more sophisticated way to keep from getting lost, using a technology that the Army made famous during Operation Desert Storm. To find their bearings in the desert landscape, soldiers relied on hand-held electronic gadgets called Global Positioning System receivers. The devices, which pick up signals from a $10 billion network of U.S. satellites, can pinpoint a location instantly anywhere on the earth.

Civilians can buy similar products from electronics companies. GPS receivers steer boaters around dangerous reefs, track schools of bait for fishermen and help pilots avoid midair collisions. The price of a receiver -- $1,500 to $3,800 -- is steep for Scout troops but falling rapidly.

The concept of the Global Positioning System is simple. With the help of an on-board atomic clock, each satellite in the network continuously broadcasts a signal indicating the time and the spacecraft's exact position. (A total of 16 satellites are now aloft; there will be 24, including three spares, when the system is completed in 1993.) A GPS receiver uses simultaneous readings from three different satellites to "fix" the user's longitude and latitude.

Relying on satellites rather than ground stations makes the system far more precise than conventional navigation technology. The loran systems commonly found on boats and airplanes, for example, are accurate only to within 100 m (330 ft.), compared with 15 m (49 ft.) for GPS.

California's department of transportation is testing a GPS dispatching system on a tow-truck fleet in the San Francisco Bay area. University of Wyoming scientists plan to use GPS technology in a tracking collar for studying the migration patterns of elk. And by combining GPS with computerized maps, engineers are developing electronic road atlases that, installed in car dashboards, could one day enable a visiting motorist to negotiate Los Angeles' freeways without ever making a wrong turn.