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The Control Segment of GPS consists of:

Master Control Station: The master control station, located at Schriever Air Force Base near Colorado Springs, Colorado, is responsible for overall management of the remote monitoring and transmission sites. As the center for support operations, it calculates any position or clock errors for each individual satellite, based on information received from the monitor stations, and then "orders" the appropriate ground antennas to relay the requisite corrective information back to that satellite.

Control Segment

Monitor Stations: Five monitor stations are located at Schreiver Air Force Base in Colorado, Hawaii, Ascension Island in the Atlantic Ocean, Diego Garcia Atoll in the Indian Ocean, and Kwajalein Island in the South Pacific Ocean. Each of the monitor stations checks the exact altitude, position, speed, and overall health of the orbiting satellites. The control segment uses measurements collected by the monitor stations to predict the behavior of each satellite's orbit and clock. The prediction data is up-linked, or transmitted, to the satellites for transmission back to the users. The control segment also ensures that the GPS satellite orbits and clocks remain within acceptable limits. A station can track up to 11 satellites at a time. This "check-up" is performed twice a day, by each station, as the satellites complete their journeys around the earth. Variations, such as those caused by the gravity of the moon, sun and the pressure of solar radiation, are noted and passed along to the master control station.

Ground Antennas: Ground antennas monitor and track the satellites from horizon to horizon. They also transmit correction information to individual satellites.

Next: Space Segment

GPS/WAAS Information Copyright © 2005 Federal Aviation Administration
For more information, visit gps.faa.gov. Updated by FreeFlight Systems. 2009.

 


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