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Navigation satellite systems have been a definite revolution for our civilisation in navigation, positioning, surveying, and the development of specific applications in a wide variety of fields.

Since man first needed to orient himself on voyages over land and sea, we have used the term navigation to designate the most appropriate way of determining our trajectory. In the beginning man oriented himself with the stars, then he used a compass as a guide and in the 19th Century, Marconi's radio was crucial to developing new forms of orientation.

Satellite navigation is the latest step for man in the attempt to determine his bearings. Today's satellite navigation systems allow the user to find his position, speed and time with high precision and reliability, with at least four satellites measuring his distance.

Global Navigation Satellite System (GNSS)

In 1991, the International Civil Aviation Organisation (ICAO) created a new concept; the global navigation satellite system (GNSS). One of the objectives of the ICAO is to coordinate all the current and future air navigation systems to guarantee that they operate correctly between themselves.

The GNSS systems provide important benefits:

• The air navigation strategy for the European Civil Aviation Conference (ECAC) establishes the substitution of part of the current land navigation systems for civil aviation in the near future.
• World-wide coverage and the capability to operate around the planet using just one receiver.
• Greater efficiency in the use of airspace and airports.
• Usage by other means of transport: roads, railways, maritime.

At present, the GNSS is at the first phase, which includes, among others, the two systems that are currently operative: the American GPS and the Russian GLONASS (which does not offer a completely operative service, given that at present the number of satellites in orbit is insufficient) and the four augmentation satellite-based systems: EGNOS in Europe, WAAS in the United States, MSAS in Japan and GAGAN in India.

The second phase of GNSS includes the European navigation satellite system, Galileo. Once the European constellation is up and running, although this date has yet to be confirmed, it will add innovative new services for search and rescue, safety of life and security under civil control. The global navigation satellite system will consist of thirty more satellites that will provide an unprecedented improvement in air, maritime and road navigation.