Telemetry, Tracking, and Command (TT&C)

The telemetry, tracking, and control (TT&C) subsystem of a satellite provides a connection between the satellite itself and the facilities on the ground. The purpose of the TT&C function is to ensure the satellite performs correctly. As part of the spacecraft bus, the TT&C subsystem is required for all satellites regardless of the application. This chapter describes the three major tasks that the TT&C subsystem performs to ensure the successful operation of an applications satellite: (1) the monitoring of the health and status of the satellite through the collection, processing, and transmission of data from the various spacecraft subsystems, (2) the determination of the satellite’s exact location through the reception, processing, and transmitting of ranging signals, and (3) the proper control of satellite through the reception, processing, and implementation of commands transmitted from the ground. Some advanced spacecraft designs have evolved toward “autonomous operations” so that many of the control functions have been automated and thus do not require ground intervention except under emergency conditions.