Figure 10.3.9 Electrical Architecture TT&C and Data Handling This subsystem performs the telemetry, command, ranging, and control functions. The telemetry subsystem generates the telemetry signals, which monitor the status of spacecraft, and transmits them to the Earth. The command subsystem receives the command signals from the ground station and interprets them. The ranging subsystem receives the ranging signals for orbit determination from the ground station and then returns them to the Earth. The radio frequency (RF) communication equipment required for the telemetry, command, and ranging signals consists of a telemetry transmitter, command receiver, wave guide, coax and so on. S-Band, C-Band, and Ku-Band frequency could be used for signal transmission. S-Band frequency is generally recommended for spacecraft use. If 2.45 GHz is assigned as the requency to transmit electric power, a frequency other than 2.45 GHz should be assigned to communicate for telemetry and command. The control electronics or computer (microprocessor or CPU), integrates the distributed set of the other electronics performing TT&C functions. This computer includes software programs installed in its memory beforehand to perform attitude determination and control as well as TT&C functions.
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