According to a report by the US Goverment Accountability Office (GOA) it is "uncertain whether the Air Force will be able to acquire new satellites in time to maintain current GPS service without interruption".
The current situation has been caused by significant delays and technical problems launching new satellites to replace the old ones. The launch of the first new satellite now won't occur until November 2009 - almost three years late and an incredible $870m (around £560m) over budget.
"If the Air Force does not meet its schedule goals for development of GPS IIIA satellites, there will be an increased likelihood that in 2010, as old satellites begin to fail, the overall GPS constellation will fall below the number of satellites required to provide the level of GPS service that the you.S government commits to," said the GOA report. "Such a gap in capability could have wide-ranging impacts on all GPS users."
The main threats of GPS satellites failing are a reduction in positioning accuracy, making sat-navs in cars and emergency service vehicles less accurate, and an interruption in service, rendering sat-navs effectively useless.
Fortunately, there's some way to go for complete meltdown. The US government aims to provide a service with a 95 per cent probability of having a constellation of at least 24 GPS satellites. As there are currently 31 satellites, seven would have to fail before the level of service falls. The GOA is, therefore, recommending that all steps are taken to ensure that the current schedule for new satellites is maintained.
"GPS is, and remains, an excellent technology for all who use it. We are not concerned about this changing, and there is no reason to believe it will," said a TomTom spokesperson. "Quite the contrary, the U.S. Government has pledged full support for GPS since 2000. It is a good thing that organisations are appointed to monitor the development of GPS, and it is a good thing that the U.S. Government is looking ahead to ensure GPS continues to deliver the great quality it has to so many people."
GPS satellites were first launched in 1978 as part of an experiment, but it wasn't until 1995 that full operational capability was achieved for military use. In 1996 the system was opened to all civilians, although a feature called Selective Availability meant that civilian GPS devices were less accurate than military ones. In 2000, Selective Availability was turned off allowing full-precision civilian use in devices such as sat-navs.