European Geostationary Navigation Overlay Service is being developed by european space agency (ESA) in conjunction with the European Organisation for Safety of Air Navigation. It improves the accuracy and reliability of navigation signals from the military-controlled US GPS and Russian GLONASS global satellite navigation systems to the point where they can be used for safety critical applications, such as navigating ships through narrow channels. It is due to become operational in early 2004.

EGNOS receives signals from the GPS and GLONASS satellites and, using specialised hardware, adds a correction factor which makes them accurate to five metres or better. The signals are then beamed back into space, and broadcast by the EGNOS transponders onboard Inmarsat satellites and picked up by receiving equipment, fitted into vehicles. When EGNOS is fully operational, it will have three satellites.

During early 2000, the system was used to guide a large ship to its berth in the harbour at Genoa, Italy. On another occasion, last November, a Fiat car, driven around a track in Turin, Italy, showed that EGNOS has the potential to determine position to within a metre. EGNOS should make it possible to navigate accurately within the confined channels and to identify harbour entrances to within a few metres without other navigation aids.

EGNOS shows not only greater accuracy but also greater consistency and reliability than GPS alone. The fully operational system will be capable of alerting users within less than six seconds of a malfunction of the GPS or GLONASS satellite constellations. EGNOS is a first step towards Galileo, a comprehensive European global satellite navigation system. Consisting of 30 satellites in medium Earth orbit, Galileo will be under civilian control and will provide a reliable, accurate and guaranteed satellite navigation service from 2006/8 onwards.