The telemetry, tracking, and command (TT&C) subsystem allows ground stations to monitor and control satellites. It performs functions like controlling the satellite's orbit and attitude, realigning antennas, receiving and executing commands, tracking the satellite's position, and modulating and transmitting telemetry data about things like voltage, temperature, and tank pressures to ground stations. The subsystem consists of separate telemetry, tracking, and command subsystems that work together to monitor the satellite's conditions and control it from the ground.

1. Telemetry, Tracking
& Command Subsystems
Arpan Deyasi
Dept of ECE, RCCIIT, Kolkata, India
Course: MCE203A

2. Learning Objective
Be able to understand key functionalities of
TT&C Subsystem for satellite communication
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3. It is the method to monitor and observe the
spacecraft’s conditions from ground station
Objective
Functions
Control orbit and attitude of satellite from ground station
Re-aligning of antennas
Command reception and detection
Telemetry modulation and transmission
Carrier Tracking
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4. Blockdiagramof
TT&Csubsystem
(source:Prattet.al.)
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5. Telemetry and Monitoring Subsystem
‘Telemetry’ means measurement at a distance.
Telemetry subsystem present in the satellite performs mainly
two functions −
I. receiving data from sensors
II. transmitting that data to an earth station
Most commonly monitored parameters are:
A. voltage, current and temperature of all major sub-systems
B. switch status of communication transponders
C. pressure of propulsion tanks
D. outputs from attitude sensors
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6. Tracking Subsystem
useful to know the position of the satellite and its current orbit
It has the following functions:
I. Measuring the time taken by RF signal for one complete
journey
II. Calculation of range of satellite
III. Changing of antenna position and orientation in both
Azimuthal and Elevation planes
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7. Command Subsystem
It receives commands transmitted from the satellite control
centre, verifies reception and executes these commands.
Example of common commands are:
Switching of transponder
Reconfiguration of switch matrix
Position control of antenna
Controlling speed of solar array drive
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8. References
1. T. Pratt, C. Bostian, J. Allnutt, “Satellite Communications”, 2nd Ed,
JWS, 2003
2. A. K. Maini, V. Agrawal, “Satellite Communications”, Wiley, 2019
3. https://www.tutorialspoint.com/satellite_communication/
satellite_communication_ttcm_subsystem.htm
4. https://ocw.mit.edu/courses/aeronautics-and-astronautics/
16-851-satellite-engineering-fall-2003/lecture-notes/
l20_satellitettc.pdf
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