Galileo is the informal name for the European Global Navigation Satellite System (GNSS), a system that will offer users anywhere in the world "near pinpoint" geographic positioning when it becomes fully operational by 2008. Designed to be interoperable with the other two such systems, the United States' Global Positioning System (GPS) and Russia's Global Orbiting Navigation Satellite System (GLONASS), Galileo will enable a user to take a position from any combination of satellites with a single receiver. Both GLONASS and GPS are run by the defense departments of their respective countries. Galileo will be civilian-operated.

The Galileo system, which consists of 30 satellites orbiting the earth at a height of 15,000 miles, is expected to pinpoint a geographical position to within a single meter. Because the service's availability will be guaranteed in almost any circumstance, the system will be ideal for applications in which precision and reliability are critical, such as air traffic management (among many possible examples). Galileo will also perform global search and rescue (SAR) functions, based on the Cospas-Sarsat SAR system. Each satellite will have its own transponder, which will transfer distress signals from a user's transmitter to a rescue co-ordination center. Once the rescue operation is launched, the system will transmit a signal to the user, to notify them that help is on the way.

When fully deployed, the Galileo system will use 27 operational satellites and three spares for failover redundancy. The satellites will be positioned in three circular Medium Earth Orbit (MEO) planes 15,000 miles up, at an inclination of 56 degrees relative to the equatorial plane. Two Galileo Control Centers (GCC) will be located in Europe; these centers will receive data from a global network of twenty Galileo Sensor Stations (GSS). GSS data will allow the control centers to synchronize the time signals of satellites with the ground station clocks, and to calculate data about system integrity. Five S-Band (2.0-4.0 GHz) and 10 C-Band (4.0-8.0 GHz) uplink stations around the globe will manage the flow of data between the satellites and the control centers.

Galileo is named for the Italian astronomer, mathematician, and physicist, Galileo Galilei. In the 16th and 17th centuries, Galileo applied mathematics to the study of physical science. This new approach, coupled with discoveries through the telescope, revolutionized both astronomy and the study of motion. Galileo is also the name of an unmanned American spacecraft sent to explore Jupiter and its moons in the mid-to-late 1990s.

This was last updated in May 2007

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