Galileo sensor stations, reversing the way satellite navigation usually operates, work together to pinpoint a Galileo satellite’s orbital position, its clock rate and signal health. Sensor station data gets fed through to the twin Galileo control centres so a set of corrections can be compiled. These corrections are uplinked to the satellites by Uplink stations every 100 minutes or less, for rebroadcast within the Galileo signal, keeping the system sufficiently aware. Telecommands to the satellite platforms are uplinked by dedicated Telemetry, Tracking and Command (TT&C) stations.