Telemetry system The telemetry, tracking, and command (TT&C) subsystem performs several routine functions abroad a spacecraft. The telemetry or "telemetering" function could be interpreted as "measurement at a distance“. Specifically, it refers to the overall operation of generating an electrical signal proportional to the quantity being measured, and encoding and transmitting this to a distant station, which for satellite is one of the earth stations.

The main functions of TT&C are: 1) Monitor the performance of all the satellite sub-systems and transmit the monitored data to the satellite control center. 2) Support the determination of orbital parameters. 3) Provide a source earth station for tracking. 4) Receive commands from the control center for performing various functions of the satellite.

TT&C Data that are transmitted as telemetry signals include attitude information such as obtained from sun and earth sensors; Environmental information such as magnetic field intensity and direction, the frequency of meteorite impact and so on ; and Spacecraft information such as temperatures, power supply voltages, and stored fuel pressure.

Summary of the parameters monitored by the Telemetry system are: 1) Voltage, current and temperature of all major sub-systems. 2) Switch status of communication transponders. 3) Pressure of the propulsion tanks 4) Outputs from altitude sensors. 5) Reaction wheel speed

Command systems: Command system receives instructions from ground system of satellite and decodes the instruction and sends commands to other systems as per the instruction. Example of commands are: 1) Transponder switching 2) Switch matrix configuration 3) Antenna pointing control 4) Controlling direction and speed of solar array drive 5) Battery reconditioning 6) Beacon switching 7) Thruster firing 8) Switching heaters of the various sub-systems

Answer for Puzzle 1. Stormy (on Tree) 2. Puddle (on boys Raincoat) 3. Wet (on Purple Umbrella) 4. Showers (on Orange Umbrella) 5. Damp (on the Drain) 6. Clouds (on the bush below Cloud)

Tracking : Tracking of the satellite is accomplished by having the satellite transmit beacon signals which are received at the TT&C earth stations. Tracking is obviously important during the transmitter and drift orbital phases of the satellite launch. When on-station, a geo-stationary satellite will tend to shifted as a result of the various distributing forces, as described previously. Therefore it is necessary to be able to track the satellites movements and send correction signals as required. Satellite range is also required for time to time. This can be determined by measurement of propagation delay of signals specially transmitted for ranging purposes.