Two satellite-based navigation systems for the high precision positioning of aircraft, ships, trucks are operational today: the US's Global Positioning System (GPS) and Russia's Global Navigation Satellite System (Glonass). Both are military oriented networks, each based on similar constellation of nominally 24 operational satellites.
Europe decided to implement a satellite-based navigation system in a two-step approach. The first step led to a European overlay navigation system (EGNOS) based on existing navigation satellites constellations. The second step (Galileo) is enabling Europe to set up its own civilian satellite navigation service.