Friday August 20 3:30 AM ET

Satellite Navigation Tool in Trouble

Full Coverage Global Positioning System

By DARA AKIKO WILLIAMS Associated Press Writer

MARINA DEL REY, Calif. (AP) - For those who rely on the high-tech Global Positioning System to find their way around, this weekend has plenty of potential drama.

The satellite-based navigation devices in use all over the world could malfunction when the system resets its clocks at 5 p.m. PDT Saturday.

That could be a problem for someone such as Stuart Prince, a boater who relies on his GPS. Prince doesn't carry maps or charts when he sails off the Southern California coast. He has no radar on his 30-foot sailboat and doesn't know how to navigate by the stars.

``I guess I'd just go east until I hit land,'' Prince, 39, said as he and a buddy fiddled with his GPS receiver. ``It's such a fantastic tool. Everyone is so dependent on it.''

Because of this possible Y2K-like glitch, the receivers may take longer to pinpoint a location, be off in their calculations or be unable to find a location, which is usually displayed on a map or in latitude and longitude.

The reason for the problem is that GPS receivers determine a location by using signals from three to 24 satellites. To account for variations in the Earth's orbit and rotation, they need the exact time, determined by counting the weeks since Jan. 5, 1980 - up to 1,024.

GPS is reaching its maximum number of weeks and time clocks on the locators are resetting to zero.

Most receivers built since 1993 were designed to handle the rollover. Manufacturers have offered upgrades of older ones.

A nationwide boat rescue company, Vessel Assist Association of America, doesn't expect an increase in calls a day for help. But finding a stranded boat's exact coordinates might take a little longer.

``If there would be a problem, then we're going to have difficulty in finding people because we rely on them to tell us where they are - and they use GPS to do that,'' said Vessel Assist spokesman Brian Haney.

If needed, the company can locate a boat using VHF radio frequencies.

GPS, originally designed for the military, has been used for at least a decade by aviators and boaters.

Now the devices are booming in the commercial market, often offered in luxury cars as a mapping device. Hikers use GPS to recall a favorite campsite or apply it like a high-tech trail of bread crumbs to get back to their starting point in featureless terrain or bad weather.

Hand-held GPS units are hot-selling gadgets at sporting goods stores, priced between $100 and $750.

Gretchen Crumbaugh, 28, of Boulder, Colo., has used GPS while hiking in the Rockies but places her faith in her compass and topography map.

``I think of it as a toy,'' she said. ``We've taken it hiking a few times to say, `Hey, we got up to 10,000 feet.'''

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Ray

-- Ray (ray@totacc.com), August 21, 1999