Air Force waves off warnings about GPS accuracy

NEW YORK -- A government report says the accuracy of GPS signals could deteriorate in the next few years because of delays in satellite launches, but the Air Force says it has plenty of ways of keeping up the navigation system increasingly relied on by drivers and cellphone users.

The Government Accountability Office reported last month that there is a risk that launches of new satellites will not keep pace with the wear and tear on the Global Positioning System.

That could mean that the accuracy and reliability of hundreds of millions of civilian and military GPS devices — including everything from "buddy finder" cellphone applications to guided bombs — could degrade until new satellites are in orbit.

The next generation of GPS satellites, dubbed IIF, has been beset by launch delays and budget overruns. Contractor Boeing Co. said the delays were due to design changes necessary to ensure that the satellites would last. The work is now done, and the first IIF is slated to launch in November, nearly three years behind schedule.

The GAO, the investigative arm of Congress, said the chief risk is that the following generation of satellites, IIIA, will be delayed in a similar fashion. Lockheed Martin is building that series, and the first are scheduled to launch in 2014.

Though it's now in widespread civilian use, GPS was originally developed for the military, and it's still managed by the Air Force.

The Air Force's mission is to maintain a "constellation" of 24 working satellites, virtually ensuring that at any time there are at least four in the sky above any point on the Earth. That's the minimum number needed for a GPS device to compute its location by measuring the slightly different amounts of time it takes for radio signals to reach it from each satellite.

The satellites don't work forever: A few launched in the early '90s are still in operation, but most have shut down. The delayed launch of the IIF series means that for a few years, satellites could be failing faster than they're being replaced.