reference in time and space.
More and more often, it will become
necessary to ascertain one's precise position in space and time in a
reliable manner. This will be possible with the
GALILEO satellite radio navigation system, an initiative launched by the
European Union and the European Space Agency. This worldwide system will
ensure complementarity with the current GPS system.
radio navigation is an advanced technology. It is based on the
emission from satellites of signals indicating the time
extremely precisely. This enables any individual to determine
his or her position or the location of any moving or
stationary object (e.g. a vehicle, a ship, or a herd of
cattle, etc.) to within one metre thanks to a small cheap
GALILEO is based on a constellation of 30 satellites
and ground stations providing information concerning the positioning of users in
many sectors such as transport (vehicle location, route searching, speed
control, guidance systems, etc.), social services (e.g. aid for the disabled or
elderly), the justice system and customs services (location of suspects, border
controls), public works (geographical information systems), search and rescue
systems, or leisure (direction-finding at sea or in the mountains, etc.).
navigation - How does it work ?
time immemorial, people have looked to the heavens to find their way. Today,
satellite navigation is continuing this tradition, while offering, thanks to
leading-edge technology, an accuracy far beyond that possible by simply
observing the sun and the stars. This technology, which has been developed over
the last thirty years or so, essentially for military purposes originally,
enables anyone with a receiver capable of picking up signals emitted by a
constellation of satellites to instantly determine their position in time and
space very accurately.
operating principle is simple: the satellites in the constellation are fitted
with an atomic clock measuring time very accurately. The satellites emit
personalised signals indicating the precise time the signal leaves the
satellite. The ground receiver, incorporated for example into a mobile phone,
has in its memory the precise details of the orbits of all the satellites in the
constellation. By reading the incoming signal, it can thus recognise the
particular satellite, determine the time taken by the signal to arrive and
calculate the distance from the satellite. Once the ground receiver receives the
signals from at least four satellites simultaneously, it can calculate the exact