Mission Control Center, Houston sends commands and receives telemetry via the 60-ft. diameter, high-gain microwave ground terminals at NASA's White Sands Test Facility near Las Cruses in southern New Mexico. It uses the S-band and UHF frequencies, as well as the early ISS communications system.
The terminals relay signals to and from a pair of Tracking and Data Relay Satellite System satellites orbiting at an altitude of 22,300 miles. The satellites pass the signals directly to and from the U.S. segment of the ISS at a rate equivalent to sending the contents of the entire encyclopedia Britannica every second.
Commands can also reach the station through a docked Space Shuttle and through the Russian communications system. Russian coverage is nearly continuous while using Russian ground stations, which are available for a portion of an orbit. Russia's launch tracking and data relay satellite provides coverage for about 45 minutes per orbit.
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