Ephemeris data from a satellite is considered to be valid for four hours (the transit time from horizon to horizon), but is in any case updated after two hours.
Satellite ephemeris data. Data broadcast by the GPS satellite containing very accurate orbital data for that satellite, atmospheric propagation data, and satellite clock error data.
The satellite then broadcasts this updated position information, known as ephemeris information, with its signal. Your GPS receiver decodes that signal, making it possible to determine exactly where each satellite really is at any time.
  
|
RSS
