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Computer Sky-Track Tells Where You Are

BOGGED down in traffic, you're figuring on a 40-minute delay when the screen on your dashboard flashes. You punch a button. An on-board computer checks the congestion and charts another route that will save 10 minutes. The route isn't familiar, so a synthesized voice tells you when to make the turns.

Twenty-first century stuff? Not at all.

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Next January, General Motors will outfit 100 of its Oldsmobile Toronado Trofeos with a version of this system. Mazda and other Japanese carmakers already sell early versions in Japan.

Hungry for spicy food? The computer's electronic "Yellow Pages" locates the nearest Mexican restaurant and tells you how to get there.

To do all this, scientists, governments, and private companies have been looking for a foolproof way to answer that basic human question: "Where am I?" Once people know where they are, it's almost always easier to get where they're going.

Technology has made rapid strides in the last 50 years to answer the question. Allied bombers pioneered the use of radar to locate their position during World War II. Many a sailor has stayed the course using a ground-based system called LORAN-C. The Japanese and Europeans are experimenting with electronic beacons along the roadside. Some United States trucking companies use two satellites to locate their drivers.

The most ambitious project of all is something called the Global Positioning System or GPS.

Sometime in 1993, humans will look to the sky - to a man-made constellation of 21 satellites circling the earth - to find their way. (Fifteen satellites are up already.) When all are in place, anyone anywhere will be able to use a simple receiver to locate his or her position to within 20 to 30 meters (22 to 33 yards). Already, surveyors are using a second receiver to pinpoint their location to within centimeters.

Unlike ground-based systems, the technology can find a point in three-dimensional space. Thus, an air-traffic controller could reduce the standard separation between planes, making takeoffs and landings more frequent and increasing airport capacity. Pilots could fly the most efficient and fuel-saving routes, rather than the restrictive ones now in place.

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Other possibilities: A dispatcher reroutes his truck fleet more efficiently. Children find their way to school with a small receiver in their backpacks, which sounds a loud warning if they stray off course; hikers pack a GPS receiver when they hit the trail.

Not everyone thinks GPS is the wave of the future. But Steven Colwell, chairman of the newly formed Global Positioning System Association, says the technology could be as revolutionary as the personal computer. The system works by receiving signals from four satellites. Each signal tells the satellite's position and the time it was sent. The computer calculates the time it received the signals, then calculates the location.

The US military developed the system in the '70s to track its far-flung forces. When it ran short of its own receivers during the recent war with Iraq, it scrambled to buy them from private companies. Under current rules, the military can degrade the satellite signals and make commercial receivers up to 10 times less accurate than military ones.

The US Department of Defense would like to keep that control, known as Selective Availability. Private GPS companies and other government agencies are fighting it.

Already, Northwest Airlines has equipped one of its Boeing 747s with GPS, and a similar Soviet system called GLONASS tracks commercial air corridors over the Soviet Union. The US Federal Aviation Administration is taking a hard look at using GPS for tracking and routing aircraft, with an eye toward cutting back its ground-based systems. The US space agency plans to launch a spacecraft outfitted with GPS this year.

Whether GPS succeeds commercially depends on how cheap and reliable it becomes. (The satellite signals bounce around among tall buildings in large cities.) There's also a caveat. George Orwell envisioned a society under constance surveillance in his landmark book "1984." Policymakers will have to ensure that governments don't turn this "Where-am-I?" technology into a "Where-are-you?" tool for Big Brother.

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