Galileo constellation

What is Galileo?

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ESA / Applications / Navigation / Galileo / First Galileo Launch

Galileo will be Europe’s own global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civilian control. It will be inter-operable with GPS and GLONASS, the two other global satellite navigation systems.

A user will be able to determine their position with the same receiver from any of the satellites in any combination. By offering dual frequencies as standard, however, Galileo will deliver real-time positioning accuracy down to the metre range, which is unprecedented for a publicly available system.

It will guarantee availability of the service under all but the most extreme circumstances and will inform users within seconds of a failure of any satellite. This will make it suitable for applications where safety is crucial, such as running trains, guiding cars and landing aircraft.

The first Galileo satellite will be launched at the end of December 2005, followed by a second in 2006. The mission objective of these satellites is to characterize the critical technologies which have been developed under ESA contracts. Following on from this first in-orbit validation of Galileo technologies, four operational satellites will be launched to complete validation of the basic Galileo space segment and the related ground segment. Once this In-Orbit Validation (IOV) phase has been completed, the remaining operational satellites will be placed in orbit to reach full operational capability.

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 with each orbital plane inclined at 56 degrees to the equatorial plane. Once this is achieved, the Galileo navigation signals will provide a good coverage even at latitudes up to 75 degrees north, which corresponds to the North Cape, and beyond. The large number of satellites together with the optimisation of the constellation, and the availability of the three active spare satellites, will ensure that the loss of one satellite has no discernible effect on the user.