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Friday, January 22, 2021

What is Galileo?

Galileo will ensure Europe's independence in a sector that has become critical for its economy and the well-being of its citizens. 

Galileo is Europe’s own global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civilian control. It is inter-operable with GPS and Glonass, the US and Russian global satellite navigation systems.

By offering dual frequencies as standard, Galileo will deliver real-time positioning accuracy down to the metre range. It will guarantee availability of the service under all but the most extreme circumstances and will inform users within seconds of any satellite failure, making it suitable for safety-critical applications such as guiding cars, running trains and landing aircraft.

A range of services will be extended as the system is built up from IOC to reach the Full Operational Capability (FOC) by this decade’s end.


The fully deployed Galileo system consists of 30 satellites (27 operational + 3 active spares), positioned in three circular Medium Earth Orbit (MEO) planes at 23 222 km altitude above the Earth, and at an inclination of the orbital planes of 56 degrees to the equator.

Control stations

Two Galileo Control Centres (GCCs) have been implemented on European ground to provide for the control of the satellites and to perform the navigation mission management. The data provided by a global network of Galileo Sensor Stations (GSSs) will be sent to the Galileo Control Centres through a redundant communications network. The GCCs will use the data from the Sensor Stations to compute the integrity information and to synchronise the time signal of all satellites with the ground station clocks. The exchange of the data between the Control Centres and the satellites will be performed through up-link stations.


The last decade augmentation systems are developed to correct for certain errors (e.g. satellite clock error, atmospheric errors) that influence the accuracy of GNSS signals. These systems are known under the term ‘SBAS’ which stands for ‘Satellite based augmentation-systems’. Several countries (USA, Japan, India) have developed their own system and Europe developed the European Geo-stationary Navigation Overlay Service (EGNOS). The system started its initial operations in 2005 but the official start of EGNOS operations as an ‘open service’ was announced by the European Commission in October 2009.

Within a satellite based augmentation system a network of ground reference stations and geostationary satellites is used to collect the error data, send a correction message to a geostationary satellite that subsequently re-transmits the signal, which can then be received like a normal GNSS signal, which is more accurate than the ‘traditional’ signal. EGNOS consists of transponders aboard three geostationary satellites over the eastern Atlantic Ocean and Europe, linked to a network of about 40 ground stations and four control centres. The ground control centres process and correct the data and information on the accuracy and reliability is send to EGNOS satellites for transmission to end-user devices. EGNOS corrections can improve the accuracy of current GPS services from 10 m to about 2 m. The EGNOS coverage area is Western Europe, but could be readily extended to include other regions within the broadcast area of the geostationary satellites, such as Africa, Eastern European countries, and Russia.

Other EGNOS data services

For some applications, broadcasting of the signals via geostationary satellites may have some limitations due to obstacles in the nearby environment or landscape. Therefore, a different transmission link may be needed to take full advantage of the EGNOS potential. ESA launched an internal project to provide access to these messages through the Internet. This project is called SISNeT (Signal In Space Through The Internet). SISNeT gives access to the wide-area differential corrections and the integrity information of EGNOS. Since February 2002, the system has been operational, broadcasting an EGNOS signal through the Internet, as generated by the EGNOS System.

In addition to SISNeT, the EGNOS Data Access Service (EDAS) provides all EGNOS raw measurements and the generated correction messages. It is available through a ground network without requiring direct access to an EGNOS satellite. It can therefore be used in constrained environments such as when signals are blocked or are disturbed by interference.

EGNOS in agriculture

With the development of precision agriculture, more use is made of aerial images, sensors and satellite navigation systems in both arable and livestock farming. The use of new techniques with an increasing accuracy aims at increasing productivity, making more efficiently use of resources while reducing impact on the environment. Galileo and EGNOS can be used in a wide variety of agricultural applications, benefitting from the improved accuracy it provides. The promotional video on EGNOS below shows several applications that make use of this service.


Galileo Timeline

The Galileo satellite constellation will be ready and fully operational by the end of 2019.

 2014 3rd quarter Launch of two full operational Galileo satellites
 2014 Summer
Launch of two full operational Galileo satellites
 2014 February Test of the SAR function (Search and Rescue)

77% of simulated distress locations can be pinpointed within 2 km, and 95% within 5 km. Tested with 4 Galileo satellites. This function operates as part of the International Cospas-Sarsat Programme.

 2013 March 12 First position fix with Galileo in ESA-ESTEC Center in Noordwijk, The Netherlands
Funding secured for EGNOS and Galileo for the new financial framework 2014-2020
  The IOV step has been completed in 2013.
October 12
Launch of two IOV satellites
 2011 October 21
Launch of two IOV satellites

These four satellites, launched in respectively 2011 and 2012, are required to do an in-orbit validation (IOV).

 2008 December Launch of the second test satellite GIOVE-B
 2005 April Launch of the first test satellite GIOVE-A
  The GIOVE-A and B were launched to test the new Galileo technology. GIOVE-A was launched to claim the frequencies allocated to Galileo by the International Telecommunications Union (ITU). GIOVE-B was the first satellite to actually transmit Galileo signals.
 2003   Validation of critical algorithms


Facts of Galileo

  • 27 in-orbit satellites + 3 spares
  • Orbital altitude: 23,222 km
  • 3 equally spaced orbital planes
  • Orbital inclination of 56°
  • 9 orbital satellites and 1 spare in each plane
  • Orbital revolution period of 14 hours and 22 minutes
  • Satellite lifetime: >12 years
  • Satellite mass: 675 kg
  • Satellite body dimensions: 2.7 m × 1.2 m × 1.1 m\
  • Power of solar arrays: 1.5 kW (end of life)

UNIFARM is carried out in the context of the Galileo FP7 R&D programme supervised by the GSA (Nr. 287206)