Page 44 - SATELLITE AND RADAR COMMUNICATION SYSTEM

Tracking refers to the determination of the current orbit, position and
movement of the spacecraft. The tracking function is accomplished by

a number of techniques, usually involving satellite beacon signals that
are received at the satellite TTC&M earth station. The Doppler shift of

the beacon (or the telemetry carrier) is monitored to determine the
rate at which the range is changing (the range rate). Angular
measurements from one or more earth terminals can be used to

determine spacecraft location. The range can be determined by
observing the time delay of a pulse or sequence of pulses transmitted

from the satellite. Acceleration and velocity sensors on the satellite can
be used to monitor orbital location and changes in orbital location.

Command is the complimentary function to telemetry. The command

system relays specific control and operations information from the
ground to the spacecraft, often in response to telemetry information
received from the spacecraft. Parameters involved in typical command

links include: • changes and corrections in attitude control and orbital
control • antenna pointing and control • transponder mode of

operation, and • battery voltage control.

Tutorial 2c

The Telemetry, Tracking, Command and Monitoring

(TTC&M) system is essential to a successful operation of

a communication satellite. Draw a complete block

diagram of the satellite subsystem and write the func-

tion of the TTC&M block.

36

Satellite System Elements