GPS constellation
From GeoWiki
The current GPS constellation consists of 29 Block II/IIA/IIR/IIR-M satellites.
GPS constellation and individual satellite status is updated every working day.
Block I are referred to as the original concept validation satellites developed by Rockwell International and reflect various stages of system development.
The first Block II satellite was launched in February 1989; the most recent Block IIR-M satellite was launched on September 26, 2005.