Satellite TTC: Telemetry Tracking and Command

Satellite Telemetry, Tracking, and Command (TTC) systems are essential for monitoring and controlling satellites. These systems ensure continuous communication between ground stations and satellites, enabling precise management of satellite health and performance. TTC functions play a crucial role in maintaining the stability and operational efficiency of satellite networks.

Functions of Satellite TTC

Following are the functions of TTC in satellite communication:

• The TTC subsystem makes it possible to establish communication to and from spacecraft (i.e., satellite) from the ground.
• It is used to observe and control spacecraft’s functions and conditions from the ground.
• The telemetry system is used to report the status of on-board subsystems to the ground station.
• Carrier Tracking
• Ranging
• Command reception and detection
• Telemetry modulation and transmission

Figure 1: Block diagram of TTC system

The figure above (Figure 1) depicts a block diagram of a TTC system. As shown, there are two parts: one at the satellite or spacecraft and the other at the ground station.

As shown, the telemetry system consists of various electronic sensors for the measurement of radiation levels, temperature, power supply voltages, etc. It consists of digital and analog sensors. As shown, analog sensors are interfaced with a multiplexer. They are selected as per need and are converted to a digital value using an ADC (Analog-to-Digital Converter). This digital signal is modulated and RF up-converted before being transmitted using the TTC antenna.

In a similar way, digital transducers are interfaced with a digital MUX (Multiplexer). The transmitted information from the satellite is relayed back to Earth. With the received information, the ground station determines the operational status of the satellite at all times. Satellites operate on S, C, or Ku bands.

A command and control system permits the ground station to control the satellite. The control signals are formed based on different digital codes which inform the satellite what action needs to be taken. The commands are used for various functionalities such as:

• To initiate telemetry sequence
• Perform orientation of the antenna
• Activate thrusters for attitude control

In order to track and maintain the attitude of the satellite, on-board thrusters are fired from the ground station. This is done even to re-orient antennas of the spacecraft, to have maximum exposure of the solar panel to the sun, and to make corrections of the satellite based on infrared sensors.

Conclusion

Satellite TTC systems are fundamental for effective satellite management and communication. By leveraging telemetry, tracking, and command functions, these systems ensure reliable satellite operations, safeguard the satellite’s mission objectives, and support the overall health of the satellite infrastructure in space.