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.
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
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