What is TT&C?
TT&C stands for Telemetry, Tracking and Command — the three core functions that allow satellite operators to monitor and control their spacecraft throughout its operational life. Without TT&C, operators would be flying blind: unable to detect anomalies, adjust the orbit, or reconfigure payloads.
Telemetry
Telemetry is the continuous downlink of housekeeping data from the satellite: temperatures at hundreds of points on the spacecraft structure, battery state of charge, solar array current, attitude sensor readings, thruster fire events, payload status flags, and software logs. This data stream allows ground controllers and automated monitoring systems to detect anomalies before they become failures.
Tracking
Tracking determines the satellite's precise position in space. Ground stations measure the signal's Doppler shift and range (via ranging tones embedded in TT&C signals) to compute the satellite's orbit. This information feeds into orbit determination software, which propagates the trajectory and identifies manoeuvres needed to maintain the satellite in its designated slot or formation.
Command
Commands are encrypted uplink messages that instruct the satellite's on-board computer to perform specific actions: fire thrusters, switch payload modes, upload new software, point antennas, or enter safe mode. Command authentication via cryptographic keys is mandatory to prevent unauthorised control — a key cybersecurity concern for satellite operators.
TT&C frequency bands
TT&C links typically use S-band (2–4 GHz) for low-bandwidth housekeeping, sometimes combined with X-band for higher-rate telemetry from scientific or imaging payloads. Ka-band TT&C is emerging for HTS satellites to consolidate all links in the same frequency range.