GPS Satellites (GNSS – Global Navigation Satellite System)
- employs the doppler shift to assess orbit
- the “constellation”of NAVSTAR satellites is managed by the Air Force
- 31 satellites currently in multiple orbital planes http://www.gps.gov/systems/gps/space/#IIF
http://www.gps.gov/multimedia/images/constellation.jpgw
Where are they now? Use the satellite program from the Remote Sensing pages or this one below
– – realtime WAAS map here (FAA) - each satellite orbits every 12 hours moving 4 minutes earlier each day
- maintain at least 4 satellites overhead (>15 degrees above horizon) at all times (how high is the orbit?)
- 4 atomic clocks with precision greater than 10^-9 (?general relativity )
- GLONASS – the Russian GNSS, Galileo – European Union, and BeiDou (big dipper) – China are the other systems.
- PLUS other satellites to broadcast information (and corrections) about current location and operation of the network to ground and airborne users.