A long, long time ago in a land far, far away, (1986 Colorado Springs), I got an indoctrination into the GPS system while doing some testing of the GPS Control Segment then being installed east of Colorado Springs at Falcon AFS. Since then, I have been closely associated with the satellite business even after retiring from active duty in 1994. So I thought I would see how the GPS Systems was doing given how just about every piece of electronics I have on the boat depends on GPS for something. Here is what I found.
31 active satellites, 6 spares plus 2 recent launches in test (24 satellites required for full operational capability).
b. Oldest operational satellite launched 11-26-1990
c.Newest operational satellite launched 3-25-2015
d.Last satellite launch 10-31-2015
9 of the active satellites and 2 spares were launched since 2010 (Block IIF satellites)
f.1 more of the current generation (Block IIF) to be launched in early 2016.
g.Block III satellites (8 currently under contract) have an earliest launch date sometime in 2017
So it looks like the constellation is pretty healthy as long as the US Govt continues to fund the program at reasonable levels. The good news is we have been able to manufacture satellites that last a lot longer then originally thought and have refined the techniques on how to "fly them" to make the fuel last as long as the electronics. Originally, I think the projected life of the Block IIA satellites was 10 years. Today one of the current operational satellites and 4 of the spares are still IIA satellites ranging in age from 18 to 25 years. (The Almanac : GPS World
Sometimes we have to remember that Government does occasionally have successes. I wonder how many people with cell phones today understand GPS, how it got there, and why it works.