Recently someone I know sent me an email titled “GPS in trouble?”, asking me if I had any information about what happened.  He was responding to numerous news reports over the past weeks with headlines such as “GPS satellite system ‘close to breakdown’ and could fail by 2010 – leading motorists straight into trouble” and “GAO-Predicted GPS Failure Could Have Drastic Consequences“.  So what is going on?  Have things changed recently with this marvel of a positioning and navigation system and is it on its way to failure?

For those in the know, this is not new news.  It is true that GPS service could begin to degrade in the next several years. This is because many of its satellites are quite old and getting older, and expected new satellites have not been Photo of Johnlaunched to replace them.  Today there are 30 satellites in operation.  A 31st satellite is also in orbit, having just been launched, but it is not yet ready for service.  Of these 31 satellites, 12 were built by Rockwell called the Block II and IIA.  These satellites were built to last for 7.5 years, but in fact they have lasted much longer, with lifespans ranging from 11 to 18 years.  The other 19 satellites are the new Block IIR satellites built by Lockheed Martin and nearly all of them have been operating for less than their ten-year design life.

For the US to continue to provide service to users, they must maintain a program of launching satellites to replace the older satellites.  This begins with the launch of the newest series of satellites, 12 in all, called the Block IIF, built by Boeing.  But this development is grossly behind schedule.  For example, in 2006 the US Air Force announced the first Block IIF satellite would be launched in 2008.  This did not occur, and we continue to have a year-for-year slip on this program.  Meanwhile the existing constellation continues to age.

The Government Accountability Officegaotitle was asked to audit GPS by a Congressional committee, and in doing so discovered this potential gap in service. They issued their report which was picked up by the media, who is now reporting the sky is falling. I believe the potential is real that GPS service will degrade from current levels, but by how much is unknown. So much depends on how the old satellites perform and what kind of heroic efforts the satellite operators make to keep them running.  The US Air Force has been very good at getting useful service out of the aging satellites, and I expect that even some of the “retired” satellites could be returned to service if so needed.

As far as launching the new satellites, this will not happen quickly. The Block IIF schedule continues to slip, and the first launch is not expected to occur before next year.  Once the first satellite is up, it will take several years to step through the launch of the remaining eleven satellites.  The issue then is the 12 Block II/IIA satellites.  Will they last long enough to provide enough time for the replacement Block IIF satellites to launch?  Or conversely will the developer be able to complete the development of the Block IIF satellites soon enough so they may be launched and prevent the projected gap in service?  Only time will tell.  So we will have to take a wait and see attitude, and hope this latest report by the GAO will spur the completion of these newest satellites.

2 Responses to “What’s going on with GPS?”

  1. on 24 May 2009 at 12:24 pmTed Driver

    John,
    Good article. I did some analysis to show just what kind of impacts we could expect were we to lose from 1-9 of the most vulnerable satellites, and have no further launches. It’s not as bad as it seems.
    http://blogs.agi.com/navigationAccuracy/?p=196
    Ted

  2. on 26 May 2009 at 6:37 pmJohn Lavrakas

    Ted
    Thanks for this helpful info. For ordinary users (4 satellites in view, 5 degree mask), it indeed appears to have small impact. I expect there will be larger impact for urban dwellers, aviation users, and precision users, however, whose demands are more stringent.
    John

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