I am trying to find how many caesium atomic clocks are carried by each of the GPS satellites. And whether the satellites also carry other atomic clocks, such as rubidium or hydrogen clocks.
https://science.nasa.gov/science-news/science-at-nasa/2002/08apr_atomicclock/: "Each of the 24 GPS satellites carries 4 atomic clocks on board." Maybe something has changed since then.
EDIT (10/01/17):http://space.skyrocket.de/doc_sdat/navstar-2.htm : "GPS-2 (Global Positioning System) or Navstar-2 (Navigation System using Timing And ranging) are improved satellites of the second generation of the GPS navigation system...Each spacecraft carried 2 rubidium and 2 cesium clocks."
EDIT (10/01/17): @MartinBeckett : the following document seems recent: ftp://tycho.usno.navy.mil/pub/gps/gpsb2.txt "The design life of the Block II/IIA satellite is 7.3 years; each contain four atomic clocks: two Cesium (Cs) and two Rubidium (Rb)...The design life of the Block IIR satellite is 7.8 years; each contains three Rb atomic clocks"