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There is growing concern that GPS performance may soon start to degrade, as the Air Force struggles to keep its constellation of aging satellites in operation.
It’s been more than 30 years since the first GPS satellite was launched. Since then, the constellation has been enlarged and updated and now has 31 satellites, rather than the 24 that were originally specified. But the oldest was launched 19 years ago, and another dozen are of the same antiquated “Block 2A” generation.
The first new “Block 2F” satellite is due to be launched in November, three years later than the Air Force’s original plan and at more than twice its original price. Meanwhile, according to the Government Accountability Office (GAO), work on the next generation—“Block 3A”—is already “off to a late start.” It describes the development schedule for Block 3A as “highly compressed,” says the target launch dates are “optimistic,” and points out that “no major satellite program in the past decade has met its scheduled goals.”
The Air Force is already squeezing as much life as possible out of the existing constellation by using older satellites as in-orbit spares, and operating them at reduced power. But even the youngest of the Block 2A is now 13 years old. With a designed life expectancy of seven years, the system’s continued operation owes a lot to luck.
What that means, according to the GAO, is that the old satellites are likely to fail more quickly than they can be replaced, yielding only an 80-percent chance of them making it through the next two years with a full constellation.
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If the “optimistic” launch program goes according to plan, things should start getting better, but if the Block 3A satellites are delayed by a couple of years, we stand only a 50-50 chance of making it through the next decade with more than 21 satellites.
Dropping to 21 satellites from 31 may compromise the accuracy, availability, and reliability of GPS, though it is difficult to accurately predict by how much. There’s probably no need to rush out and buy a sextant, but it might be a good idea to brush up your traditional harbor pilotage!
This article originally appeared in the July 2009 issue of Power & Motoryacht magazine.