EGNOS

Improving the accuracy of satellite navigation

• In pre-operational service
• Designed to be fully certified in 2009

EGNOS is the European Geostationary Navigation Overlap Service. It has been developed to work alongside existing satellite navigation systems to improve the accuracy of navigation signals. This will make EGNOS suitable for safety-critical applications such as landing aircraft or navigating a ship through a narrow channel.

The EGNOS service is broadcast via two Inmarsat communications satellites and a third European Space Agency (ESA) spacecraft, Artemis. It covers the whole of Europe. EGNOS transmits a signal containing information on the reliability and accuracy of the positioning signals sent out by GPS. It allows users to determine their position to within two metres.

During the past two years, extensive trials have been carried out with the EGNOS system. The trials have involved using test planes and helicopters for air traffic control applications. It is planned that the system will be certified in 2009 for safety critical use in air traffic management.

---

Mission facts

• EGNOS is a joint project between ESA, the European Commission and Eurocontrol - the European organisation for the safety of air navigation.
  
  
• At the moment there are two existing satellite navigation systems, the US Global Positioning System (GPS) and the Russian GLONASS system.
  
  
• EGNOS improves the accuracy of GPS and GLONASS signals from 20 metres to less than 2 metres.
  
  
• EGNOS has many duplicate systems and failsafe mechanisms so that the service can be guaranteed.
  
  
• The EGNOS global navigation satellite programme is paving the way for the European Galileo satellite navigation system.

---

Technology

EGNOS consists of three geostationary satellites and a system of ground stations.

Ranging and Integrity Monitoring Stations (RIMS) on the ground pick up signals from GPS satellites.

This data is then processed in Master Control Centres (MCC). Here, the accuracy of the original signals is determined and other factors such as electrical disturbances in the atmosphere are taken into account.

This data is incorporated into an EGNOS signal and sent via a secure communications link to the three satellites.

These satellites then relay the signal back to users on the ground giving them a much more accurate position than would be achieved through GPS alone.

UK involvement

UK companies including BT, Astrium Limited, Logica and Airsys (UK) are involved in developing the EGNOS system.