News

Current state of the GPS Satellite System

Worries about the GPS system arose in May 2009 when the U.S. Government Accountability Office (GAO) released a report saying, "It is uncertain whether the Air Force will be able to acquire new satellites in time to maintain the current GPS service without interruption. If not, some military operations and some civilian users could be aversely affected."

The satellites have a limited life, typically seven to ten years. There's no practical way to fix them once they break. Of the 59 GPS satellites launched to date, 31 are still operating. Of those 31, 17 are past their life expectancy - the oldest was launched in 1990. The problem is that 24 functional GPS satellites are required for complete global coverage. With 31 still beeping, we've got plenty of spares for the moment.

However, due to a combination of schedule slips, construction problems, and cost overruns, we haven't been launching new satellites fast enough to replace those likely to fail soon. The GAO estimated that that over the next four years or so the probability that at least 24 satellites will remain operational will be less than 95 percent, at times dipping as low as 80 percent. Having something less than 24 working satellites would mean total system failure.

24 hours after the report was released, the Air Force responded by saying that "going below 24 won't happen". This was followed up with a plan to move spare satellites closer to those expected to fail, improving current coverage, minimizing outages, and buying time to get new satellites aloft.