A new US governmental advisory board is warning that the accuracy of GPS signals in challenging areas like mountains may degrade in the next few years, with "enormous adverse impact". The current GPS system, established for the American Air Force during the cold war and now used by millions of civilians worldwide, relies on an ageing network of 30 satellites for its 10m accuracy in complex mountain terrain. But the Air Force only guarantees a provision of 24 satellites, and the chairman of the Air Force Space Command GPS Independent Review Team says even that number may be difficult to maintain. By next year, Major General Robert Rosenberg says, 11 GPS satellites will have reduced capabilities and the number of satellites in the constellation may have to be cut. That would mean unreliable coverage in mountains, canyons and other topographically complex terrain. A new GPS system ('GPS III') featuring more modern satellites is at least 6 years off, with its $1.8bn funding still awaiting approval by congress.
A European alternative to GPS, 'Galileo', is due to enter full operational use by 2012, although it's likely to require you to buy a new receiver to make use of its 4m (free) or 1m (subscription) accuracy.
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