The demise of selective availability and implications for the international GPS service

Early on May 2, 2000, selective availability (SA) — the intentional dithering of clocks on GPS satellites — was terminated. The amplitude of variations in transmitter clocks, formerly tens of meters, was reduced by orders of magnitude. These clocks are now much more predictable, with the possibility that the International GPS Service (IGS) can produce, in addition to real-time orbits, real-time clocks that are of significantly higher quality than those in the broadcast ephemeris. Furthermore, the meaning of high in “high rate ground network” to support low-Earth-orbiter (LEO) missions needs to be re-examined.