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The space shuttle orbiter communication system transfers telemetry information about orbiter operating conditions and configurations, systems and payloads; commands to the orbiter systems to make them perform some function or configuration change; documentation from the ground that is printed out on the orbiter's teleprinter or text and graphics system; and voice communications among the flight crew members and between the fight crew and ground.

This information is transferred through hardline and radio frequency links. Hardline refers to wires that connect communicating devices, and RF refers to radio signals. RF communication takes place directly with the ground or through the TDRS.

Direct communication takes place through Air Force Satellite Control Facility remote tracking station sites, also known as space-ground link system ground stations, for military missions or through STDN ground stations for NASA missions. Direct signals from the ground to the orbiter are referred to as uplinks, and signals from the orbiter to the ground are called downlinks.

TDRS communication takes place through the White Sands Ground Terminal. These indirect signals from the TDRS to the orbiter are referred to as forward links, and the signal from the orbiter to the TDRS is called the return link. Communication with a detached payload from the orbiter is also referred to as FL, and RL is the signal from the payload to the orbiter.

The orbiter communication system is divided into several smaller systems to facilitate information transfer: S-band frequency modulation, S-band phase modulation, Ku-band ultrahigh frequency, payload communications, audio and closed-circuit television.

The S-band FM, S-band PM, Ku-band and UHF systems are used to transfer information between the orbiter and the ground on RF signals in their frequency bands. The payload communication system is used to transfer information between the orbiter and its payloads either through hardline or RF links. The audio systems transfer voice communications throughout the orbiter, and the CCTV system is used for visually monitoring and recording activities. Communication security equipment aboard the orbiters provides the capability for encryption and decryption of operational data.

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