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Satellite glitch may hit yachts, private planes

By Reuters
London, 13 Aug 1999

If you are going anywhere remotely adventurous in your sailboat or private plane this month, be sure you dust off your old sextant and check the chart locker.

You could be in trouble if you have been relying on the ubiquitous hand-held satellite navigation device to plot an instant course to avoid dangerous rocks. Finding a tiny island over the horizon in your plane could also be risky.

At midnight on Aug. 21, the 24 satellites of the Global Positioning System, which provide navigational data from 11,000 miles out in space, switch their timing system back to zero.

When the GPS system started operating in January 1980 it was designed to record time for 1,024 weeks. Experts say that when the "rollover," or return to zero, happens, at 23:59:47 GMT Aug. 21, up to 1.5 million of the 10 to 15 million GPS navigational devices around the world may be unable to handle it and fail or start producing dangerously unreliable data.

The possible glitch promises to provide a dress rehearsal for the millennium computer bomb, set to explode inside an unknown number of computers at midnight on Dec. 31.

If Aug. 21 passes without serious incident, the next big technology test is less than three weeks away. Sept. 9, 1999, is recorded on some computer software as 9/9/99. But computer programmers often used a cluster of nines to signal to a program that it should switch off.

The US Air Force set up the GPS to provide precise timing and navigation data for the military. Civilian users around the world have been making increasing use of the system, which provides at least four satellites for a receiver at any time anywhere on Earth and can pinpoint a location to within 100 yards on mobile phone-like receivers.

The receivers gauge location by measuring time it takes for a radio signal to travel from the satellites.

Rollover could upset transmission of data

 

"If a GPS receiver has difficulty determining the correct date before, during and after this rollover, it may process data incorrectly. In fact users who depend on GPS data for geographic locations on land, at sea or in the air could face serious safety hazards," said John Lovell, Director of Quality at Trimble Navigation, a market leader in navigation devices.

It is not just leisure activities that are under threat. Businesses such as power and telephone utilities and even international banking use the GPS to establish accurate timing of some processes.

Experts say airlines and shipping companies are not in danger. They use more traditional methods for navigation and have cross-checking built into their processes.

Lovell, in a telephone interview from his office in Sunnyvale, California, said he is confident his company`s devices will work during the changeover, but others` may not. Some depend on compatibility of software and work with embedded chips that will not be able to interpret data correctly.

"Some GPS receivers are hidden, embedded in a host of other products from car navigation to timing devices for electric and telephone utilities, vehicle and vessel tracking, surveying, environmental protection, agriculture, mining, construction and scientific research," he said.

"I am concerned but pretty confident overall."

Experts say that in the field of navigation any GPS failure should not present a problem if sensible practices are used.

"A prudent mariner will not solely rely on GPS to determine his position. I would expect anyone operating a craft on the water to use all available means of determining where they are. The simplest form is to look, use your eyeballs, match what you see from what is on the charts," said Lt. Lee Putnam, public affairs officer at the US Coast Guard navigation center in Alexandria, Virginia (www.navcen.uscg.mil).

Putnam said depending on one navigational method never made any sense. Mariners should use the range of aids available including radio, compass and dead reckoning.

Up to 1.5 million devices in jeopardy

 

Ron Stearns, defense and aerospace analyst at Frost & Sullivan, believes the risk to the travelling public is small but reckons that around 10% of GPS receivers are susceptible to "rollover" problems.

According to the US government, there are between 10 and 15 million receivers in use worldwide.

"Boaters, private pilots and climbers all use GPS for navigation. Yes, if there is a problem with GPS rollover and any of these users is totally reliant upon GPS in a critical situation, then there is the possibility for a problem," Stearns said in an e-mail message from San Francisco.

Sensible users will not have a problem, though.

"There is a great deal of resistance to using GPS as a sole means of navigation. Experienced boaters, pilots and, I would assume, outdoor enthusiasts believe in several redundant forms of navigation, whether it be ground-based radar, a compass and paper map or a sextant," Stearns said.

Peter Dana, GPS expert at the University of Texas, said it was hard to see the problem causing accidents.

"Any sailor, pilot, climber, or hobbyist who relies on a single navigation aid has already made the fundamental mistake," he said in an e-mail. "That a few GPS receivers might not properly handle a change from 1,023 to 1,024 weeks should not be a problem. I hope that is the case during the transition from Aug. 21 to Aug. 22, 1999."

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