Delays in replacing old satellites put GPS accuracy at risk

I'm probably not alone in taking the Global Positioning System for granted. But according to a new government report, the accuracy of GPS readings could start to suffer as soon as next year, unless we get on the ball with replacing aging GPS satellites.

Mac blog TidBits draws our attention to this April 2009 report from the U.S. Government Accountability Office, warning that we could face "wide-ranging impacts on all GPS users" unless the Air Force manages to launch a series of replacement GPS satellites on schedule—something it's "struggled" to do in recent years due to "significant technical problems," problems with contractors, cost overruns, and the "lack of a single point of authority" for GPS in general.

Now, as the GAO notes (you can find the full PDF of the report right here), we currently have a "constellation" of 31 GPS satellites in orbit, and we need at least 24 in operation to maintain the level of GPS service that we're all accustomed to. But some of those satellites are approaching 20 years old, and as the GAO notes, the Air Force is almost three years late in launching the first in a series of new and improved GPS satellites.

How dire is the situation? According to the GAO report, if the Air Force keeps to its current launch schedule, the chance that we'll still have 24 working GPS satellites dips below 95 percent next year, and falls to about a 80 percent in the 2011-2012 timeframe.

Those might sound like good odds, but consider this: The GAO warns that if the Air Force falls behind on its planned deployment of next-generation GPS III satellites (the first is slated to go up in 2014) by just two years (and there's a "considerable risk" that the Air Force will fall behind, according to the GAO's report), the delay could leave us with a mere 10 percent chance of 24 working GPS satellites by 2017.

Of course, as TidBits notes, GPS service won't suddenly switch off if we fall below 24 working satellites, but accuracy will dip substantially. The GAO reports ticks off a number of possible effects, including delays and/or re-routing of intercontinental airline flights, less accurate E911 service (which lets rescue workers pinpoint your location when you dial 911 from a cell phone), and problems with missile guidance (from a military point of view).

So, what to do? For its part, the GAO recommends that the Secretary of Defense appoint a "single authority" to keep watch over the GPS system. TidBits' recommendation? Call your elected representatives, pronto, and make sure they're keeping an eye on the brewing GPS situation.

Related:
GPS Accuracy Could Start Dropping in 2010 [TidBits]