Galileo’s ground segment
All space missions are divided between their ‘space segment’ – the satellite or satellites in orbit – and their ‘ground segment’ – the stations and associated infrastructure serving them on Earth.
The sheer scale and reach of Galileo means that its ground segment has a worldwide footprint, as one of the most complex developments ever undertaken by ESA.
Stations are dotted across the entire globe to ensure the continued reliability of the time and positioning information embedded within Galileo’s signals from orbit.
They monitor the precise orbits of the satellites and the timings of their clocks, so that slight corrections or integrity warnings can be made if necessary, uplinked to the satellites for rebroadcast within the navigation signals.
The more stations there are, covering all regions of the world, the more accurate and reliable Galileo becomes.
All stations are based on European-controlled territory, which in practice equals some of the remotest locations possible, from mid-ocean islands to polar bases. The stations stay connected to the rest of the ground segment via satellite links.
Overall, the Galileo Ground Segment necessary is one of the most complicated developments undertaken by Europe, having to fulfil strict levels of performance, security and safety. For added redundancy twin two control centres, oversee different tasks:
- Ground Mission Segment (GMS) – based in the Fucino Control Centre in Italy, provides cutting-edge navigation performance at high speed around the clock, processing data from a worldwide network of stations. GMS has two million lines of software code, 500 internal functions, 400 messages and 600 signals circulating through 14 different elements.
- Ground Control Segment (GCS) – based in the Oberpfaffenhofen Control Centre in Germany, monitors and controls the constellation with a high degree of automation.
These two central sites coordinate the rest of the ground segment:
- Telemetry, Tracking and Command Stations – two, at Kiruna in Sweden and Kourou in French Guiana
- Uplink Stations – a network of stations to uplink the navigation data
- Sensor Stations – a global network providing coverage for clock synchronisation and orbit measurements
- Data Dissemination Network interconnecting all Galileo ground facilities.
Last update: 18 July 2014