Galileo comprises a constellation of 30 satellites divided between three circular orbits at an altitude of around 24,000 km to cover the Earth’s entire surface. They will be supported by a worldwide network of ground stations. At present, there are two radio navigation satellite networks: the United States GPS and the Russian Glonass systems, both designed during the Cold War for military purposes. Since the Russian system has not generated any civil applications, Galileo offers a real alternative to the de facto monopoly of GPS and offers a number of advantages over the US system:
- Galileo has been designed and developed as a non-military application, while nonetheless incorporating all the necessary protective security features. Unlike GPS, which was essentially designed for military use, Galileo therefore provides, for some of the services offered, a very high level of continuity required by modern business, in particular with regard to contractual responsibility;
- It is based on the same technology as GPS and provides a similar – and possibly higher – degree of precision, thanks to the structure of the constellation of satellites and the ground-based control and management systems planned;
- Galileo is more reliable as it includes a signal integrity message informing the user immediately of any errors. In addition, unlike GPS, it will be possible to receive Galileo in towns and in regions located in extreme latitudes;
- It represents a real public service and, as such, guarantees continuity of service provision for specific applications. GPS signals, on the other hand, in recent years have on several occasions become unavailable on a planned or unplanned basis, sometimes without prior warning.
Nonetheless, Galileo also complements GPS insofar as:
- Using both infrastructures in a co-ordinated fashion (double sourcing) offers real advantages in terms of precision and in terms of security, should one of the two systems become unavailable;
- The existence of two independent systems is of benefit to all users since they will be able to use the same receiver to receive both GPS and Galileo signals.
The applications prospects are enormous. As with the microcomputer 20 years ago or the Internet 10 years ago, it is highly likely that at the moment we can only see the tip of the iceberg. To meet all these demands, Galileo will offer several levels of service, the paid-for services contributing to the economics of the system:
- A basic level free of charge, emphasising consumer applications and general-interest services. GPS is also free for these applications but Galileo offers better quality and reliability;
- Restricted-access service levels for commercial and professional applications that require superior performance to generate value-added services.These levels range up to a highly restricted service for applications that must in no event be disturbed.
After a number of disagreements, impasses and delays along the way, the European Union and the United States finally concluded an agreement that will allow the Galileo and GPS systems work alongside each other without either interfering with its counterpart’s signals in the summer of 2004. This allowed the last system specifications to be set and for implementation to proceed in three planned phases:
| Phase | Date | Tasks |
|---|---|---|
| 1 | 2002-2006 | Consolidation of mission requirements.
Development of 2-4 satellites and ground-based components. Validation of the system in orbit. |
| 2 | 2006-2008 | Construction and launch of the remaining 26-28 satellites.
Installation of the complete ground segment. |
| 3 | from 2008 | Commercial operations. |