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A Brief History of GPS Satellites
Before we can get into a discussion of the GPS satellites, one must first understand a bit of their history. The first GPS satellites, the Navstar Block I system, began launching in 1978 and ending in 1985; the last of this set was put out of service by 1995.
Our current Block II series was what replaced it. They began launching in 1989, and have since then been continuous updated in waves, a few satellites launched here and there to replenish the stock and make the whole system more accurate. However, for all that, no GPS satellite of Block II has ever been put out of service. For a summary of these successive waves, check out the Wikipedia article on GPS satellites.
Throughout all this, a variety of companies and agencies have contributing both to the development and the construction of the satellites: it has been a very mixed effort, leading to a highly unified result that has been increasingly been used by civilians to do everything from find their lost dog to find their way across the country. However, the flourishing innovation surrounding the existence of these satellites could be in grave danger:
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So, as you might have gathered, the oldest GPS satellites currently up there and operating are upwards of 20 years old, which is certainly a long operating time for a satellite. They're getting old. They've functioned beautifully during their lifetime, but they're getting old. No matter how well something is built, long term wear and tear in the harsh environment of our upper atmosphere (GPS satellites are in a low orbit) will strain any system, and they're starting to feel it. One report put it, in oft-quoted words, that they are “close to breakdown,” putting the beginning of failure in 2010. Uh-oh.
Repairing them would be near impossible, and the GPS system has proven simply too valuable to allow to fail, leaving replacement as the only option. The US Air Force, the entity in charge here, had put plans into place to have new satellites up and running in 2007, but that date's long gone, leading to cries of neglect and bad management on their part—including by the Government Accountability Office (GAO).
It should also be kept in mind that in addition to the 24 GPS satellites currently in service, there are an additional 3 in orbit in case any of the 24 break down. Also, the Block II satellites are far from being of a uniform age: the satellites of that group that are in imminent danger of breaking down are the older ones, while the newer ones, less than half their age, have a few years left in them. A total breakdown of the system is quite unlikely in the immediate future.
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That being said and done, the US Air Force hopes that they will be able to begin replacing the satellites with the Block IIF series in early 2010, which have been built by Boeing. Cutting it a little close, to be sure, but probably not too late. Check out their complete launch schedule of Boeing satellites, including the Block IIF.
Other countries have their own GPS systems in development, which may offer some competition if our own GPS system manages to survive. The EU's own Galileo system has been generating a fair amount of buzz, as have developing systems by Russia, India and China.
So, no worries about the future. The GPS system is on track for replenishment, and there may even be a little competition on the horizon. Stay tuned for the result of the planned GPS satellite launches!