When one hears the expression GPS modernization one often thinks of improvements in GPS receiver technology. But there is another side: modernization of GPS satellites in the NAVSTAR constellation.
The first of the operational satellites, Block II/IIA, was launched on Feb. 14, 1989. There were a total of 28 launched with no launch failures; the last Block II/IIA satellite was launched Nov. 6, 1997 (see Figure 2). Of the 28 satellites 18 were still operational as of Dec. 20, 2004.