The Flight Operation Segment (FOS) is responsible for sending the telecommands to the satellites and for receiving the satellite telemetry. This service is managed from the ESA’s European Space Operations Centre (ESOC) in Darmstadt, Germany, and in Darmstadt (EUMETSAT) for Sentinel-3 routine activities.

The FOS consists of the Ground Station and Communications Network, Flight Operations Control Centre and a General-Purpose Communication Network.

The FOS provides the capability to monitor and control the satellite during all mission phases including the Flight Dynamics System facility responsible for orbit determination and prediction, and for the generation of attitude and orbit control telecommands.

The main functions of the FOS include:

• Spacecraft status monitoring. Processing housekeeping telemetry, providing information about the status of all spacecraft subsystems and attitude
• Spacecraft control. Taking control actions by means of telecommands, based on the spacecraft monitoring and following the mission plan
• Orbit determination and control. Using tracking data and implementing orbit manoeuvres, ensuring required orbital conditions are achieved
• Attitude determination and control. Using processed attitude sensor data from spacecraft monitoring and by commanded updates of control parameters through the on-board attitude control system
• On-board software maintenance. Integrating software images received from the spacecraft manufacturer (pre-launch and post-launch) into the telecommand process
• Communications. Communicating (TM/TC) with one satellite at a time.