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The GPS control
segment consists of several ground stations located around the world.
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A master control
station at Schriever Air Force Base in Colorado
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Six unstaffed
monitoring stations: Hawaii and Kwajalein in the Pacific Ocean; Diego Garcia
in the Indian Ocean; Ascension Island in the Atlantic Ocean; Cape Canaveral,
Florida and Colorado Springs, Colorado
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Four large
ground-antenna stations that send commands and data up to the satellites and
collect telemetry back from them.
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The monitor stations
track the navigation signals and send their data back to the master control
station. There, the controllers determine any adjustments or updates to the
navigation signals needed to maintain precise navigation and update the
satellites via the ground antennas. To further improve system accuracy, in
2005, the master control station added data from six monitor stations
operated by the National Geospatial-Intelligence Agency to the six GPS
monitor stations.
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