Galileo, Europe’s own Global Satellite Navigation System, constituted a major topic for decision at the ESA ministerial Council in Edinburgh last November. That Council agreed the ESA funding for the Galileo development and in-orbit validation phase subject to the EU Transport Council to approve the Galileo programme.
The EU Council, when meeting on 7 December 2001 could not immediately reach final agreement on the implementation modalities. However, the Heads of State at their summit meeting in Laeken, Belgium, reaffirmed the strategic importance they attach to the Galileo programme and welcomed the decision of the European Space Agency taken in Edinburgh. In addition, they invited the EU Transport Council to take a decision in March 2002. In the meantime, the European Parliament has expressed a favourable opinion on the continuation of the programme.
An interim structure (Galileo Interim Support Structure – GISS) has already been put in place to ensure that the technical development of Galileo is coherent with the user requirements. The GISS consists of some 30 highly qualified international staff and is located in Brussels.
The preparatory development activities have been intensified over the last few months, with the European space industry but also with the application and service industries. Critical technologies, such as atomic clocks and signal generators, are under development and work is progressing as planned. The Galileo ground segment architecture has been further refined with a view to minimise the implementation and operations cost. Moreover, a major activity on the Galileo System Test Bed will start soon. That will allow validating the novel Galileo control methodology (algorithm) in a near-real environment and will establish confidence in the performance claims.
What is Galileo?
Galileo will be Europe’s own global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civilian control. It will be inter-operable with GPS and GLONASS, the two other global satellite navigation systems. A user will be able to take a position with the same receiver from any of the satellites in any combination. By offering dual frequencies as standard, however, Galileo will deliver real-time positioning accuracy down to the metre range, which is unprecedented for a publicly available system. It will guarantee availability of the service under all but the most extreme circumstances and will inform users within seconds of a failure of any satellite. This will make it suitable for applications where safety is crucial, such as running trains, guiding cars and landing aircraft.
The first experimental satellite, part of the so-called Galileo System Test Bed (GSTB) will be launched in late 2004. The objective of this experimental satellite is to characterize the critical technologies, which are already under development under ESA contracts. Thereafter up to four operational satellites will be launched in the timeframe 2005-2006 to validate the basic Galileo space and related ground segment. Once this In-Orbit Validation (IOV) phase has been completed, the remaining satellites will be installed to reach the Full OperatœÈ÷¿l Capability (FOC) in 2008.
The fully deployed Galileo system consists of 30 satellites (27 operational + 3 active spares), positioned in three circular Medium Earth Orbit (MEO) planes in 23616 km altitude above the Earth, and at an inclination of the orbital planes of 56 degrees with reference to the equatorial plane. Once this is achieved, the Galileo navigation signals will provide a good coverage even at latitudes up to 75 degrees north, which corresponds to the North Cape, and beyond. The large number of satellites together with the optimisation of the constellation, and the availability of the three active spare satellites, will ensure that the loss of one satellite has no discernible effect on the user.
Two Galileo Control Centres (GCC) will be implemented on European ground to provide for the control of the satellites and to perform the navigation mission management. The data provided by a global network of twenty Galileo Sensor Stations (GSS) will be sent to the Galileo Control Centres through a redundant communications network. The GCC’s will use the data of the Sensor Stations to compute the integrity information and to synchronize the time signal of all satellites and of the ground station clocks. The exchange of the data between the Control Centres and the satellites will be performed through so-called up-link stations. Five S-band up-link stations and 10 C-band up-link stations will be installed around the globe for this purpose.
As a further feature, Galileo will provide a global Search and Rescue (SAR) function, based on the operational Cospas-Sarsat system. To do so, each satellite will be equipped with a transponder, which is able to transfer the distress signals from the user transmitters to the Rescue Co-ordination Centre, which will then initiate the rescue operation. At the same time, the system will provide a signal to the user, informing him that his situation has been detected and that help is under way. This latter feature is new and is considered a major upgrade compared to the existing system, which does not provide a feedback to the user.
