How much do you trust your sat-nav? Based on a report by the US Government Accountability Office, you might want to think about that because there's a chance that, as of next year, the accuracy of the system could start falling as older satellites, which need replacement, begin to fail.
Without replacement, the report says the likelihood of keeping a 24-satelite constellation (as required for global GPS coverage) in orbit will drop to under 95 per cent next year, and could fall as low as 80 per cent in 2011 and 2012 - hitting about 10 per cent in 2017! Or, to phrase that with a bit more melodrama: within two years GPS could become inaccurate enough so as to be unusable.
It's not all gloom yet, though. The US Air Force - which is responsible for maintaining GPS satellites - is set to launch a new satellite in November this year; behind schedule. We in the EU might see a solution in our own Galileo system, intended to be an alternative to GPS not controlled by any one country. The idea being that even in times of war satellites would be available, which can't be said of GPS which the US could switch off to non-US users should it wish to.
Nonetheless, it's interesting to think that a system we have become so reliant on might well fail in the not-so-distant future. I should point out, however, that even if GPS does become less accurate, there still isn't any excuse for not paying attention to the road.