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GALILEO
European Satellite Navigation System

 


 

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The programme

|User needs and service definition

|GALILEO services

|System architecture

|Programme phases


System architecture

The GALILEO system architecture will be designed in such a way as to permit:

  • Adaptation of the response to the needs of users and to market trends;

  • Minimisation of development and operating costs;

  • Minimisation of the risks, other than financial risks, inherent in a project so unusual by virtue of its scope, complexity and the challenges it poses;

  • Interoperability with existing systems, notably GPS, while at the same time maintaining autonomy and competitiveness.

The GALILEO architecture is made up of four principal components:

  • Global component

  • Regional components

  • Local components

  • User receivers and terminals

Global component

Galileo satellite constellation (c) ESAThe central component will be the global constellation of thirty satellites, distributed over three planes in Medium Earth Orbit (MEO). Within each plane, one satellite is an active spare, able to be moved to any of the other satellite positions within its plane, for replacement of a failed satellite. 

Several constellations were studied for optimisation of the space segment. The retained constellation is based exclusively on satellites in MEO orbit, which ensures a uniform performance both in terms of accuracy and availability, and which offers greater robustness in crippled mode (satellite failure). The GALILEO satellite constellation is furthermore well suited for high latitude countries and offers an improved visibility in towns and cities, while at the same time being less onerous.

The size and mass of the satellites under consideration for this type of mission will ensure optimum deployment of the constellation through multiple satellite launches (2 up to 8 satellites per launch, depending on launcher capacity and deployment constraints). The ultimate choice of launcher(s) will be made on a competitive basis and will depend on the proposed launch cost per satellite, payload capability of the launcher (number of satellites per launch), on reliability factors, and contractual conditions (insurance).

The control of the satellite constellation, the synchronization of the satellite atomic clocks, processing of the integrity signal, and data handling of all internal and external elements is performed by two redundant GALILEO Control Centers (GCC). Both of which will be located on European ground. These GCC's consist of the:

  • Orbit Synchronization and Processing Facilities (OSPF);

  • Precision Timing Facilities (PTF);

  • Integrity Processing Facilities (IPF);

  • Mission Control Facility (MCF);

  • Satellite Control Facility (SCF);

  • Services Product Facility (SPF).

Data transfer to and from the satellites is performed through a global network of GALILEO Up-link Stations (GUS), each of which combines a Telemetry, Telecommand & Tracking Station (TT&C) and a Mission Up-link Station (MUS). Further MUS's complement the global up-link capabilities.

GALILEO Sensor Stations (GSS) distributed around the globe sense the quality of the satellite navigation signal (Signal In Space SIS). The information of these stations is transmitted through a redundant GALILEO Communications Network (GCN) to the two GCC's. The information on the Signal In Space (SIS) quality, also called integrity information, is the major differentiator of GALILEO compared to other GNSS. The integrity information will be transmitted globally together with the navigation signal and thus allows the GALILEO system to be certified for Safety-of-Life applications.

Regional components

The design of the GALILEO system is such as to permit the introduction of data from regional service providers using authorised integrity up-link channels provided by GALILEO, thereby making it possible to "personalise" integrity under partnership agreements with the relevant countries. The cost of this component will be borne by the region in question.

A regional component is made up of an additional network of stations to oversee the integrity of the signals and a processing centre to provide this service.

Local components 

The GALILEO system will provide high level performance to users world-wide, even in places where there is no ground infrastructure. However, in the case of specific applications in given areas, even more demanding levels of positioning performance will be necessary or, alternatively, integration with other functions, e.g. local communications, will confer added value on the basic service.

In this way, starting from a common generic conception, it will be possible to adapt local elements to specific requirements: airports, ports, rail, roads, urban areas, etc. Furthermore, each application will need to make provision for specific cases: road tunnels, urban buildings, underground parking complexes, etc. The definition phase has enabled a preliminary conception to be formed of these local elements, and this will be elaborated further during the development and validation phase. Typically, a local element will need to ensure the onward transmission of the signal, including integrity monitoring and data processing and transmission.

Data may be transmitted to the user's receiver either via a specific link or by means of external systems: mobile communication networks (using GSM or UMTS standards), Loran-C maritime navigation system, etc. In the last mentioned instance, detailed information on the user's exact position will also be available to the operator. By means of messages linking the Terminal and the Service Centre it will be possible to confer added value on the basic service, e.g. pinpointing the location of distress calls or breakdowns.

For certain modes of transport such as aviation, the existence of a local component offering a landing service adapted to the meteorological conditions prevailing in Europe will play a key role in rationalising the existing structures and making satellite navigation more attractive economically. For this reason, the Commission is committed to promoting the necessary technical and economic studies and, if the scheme is clearly feasible, it will facilitate the organisation of a local service through the structures put in place.

User receivers and terminals

Receivers will be the crucial link in the GALILEO chain and will need to satisfy market requirements:

  • Competitive performance and costs compared with the existing systems;

  • Adequate tailoring to the needs of users (general public and the professional market);

  • Potential for change and integration of the services (e.g. communications);

  • Possibility of multi-modal use.

A wide range of GALILEO receivers will be available providing the various types of satellite radio navigation services on offer, whether or not combined with other functions. In addition, the technological potential will lead to a high degree of integration of these functions (standard "microchips" tailored to a specific function). By way of illustration the following examples may be cited:

  • GALILEO mini-terminals for use by the general public, or the incorporation of a positioning function as an integral feature in mobile telephones (UMTS standard), providing value-added services or position location facilities in the event of "112" calls (emergency services);

  • The integration of a navigation service certified under aircraft industry standards in the operational support system for aircraft pilots;

  • An in-vehicle navigation platform offering the driver combined positioning and traffic information monitoring facilities.

The challenge of the market in GALILEO receivers represents one of the major factors that will determine whether the European industry successfully takes off in this area.

last update: 10-02-2009