Galileo is Europe’s own global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civilian control. It is inter-operable with GPS and Glonass, the US and Russian global satellite navigation systems.
Navigation beacons must be as visible as possible. So 20th century radio navigation towers guiding aircraft stood hundreds of metres tall, while the lighthouses guarding mariners of treacherous waters reach dozens of metres in height or cling to high ground. In essence navigation satellites are the same, except they are built on the ultimate high ground of space, making them visible from anywhere on Earth.
Goals of UIC participation in GALILEO project:
The Galileo Railway Applications Expert Group’s main activity is to follow up on matters relating to the certification and validation of Galileo for railway applications in the safety and non-safety area and to act in accordance with the mandate given by the UIC Executive Board to represent the railway viewpoint in contacts with EU projects and with the Galileo Joint Undertaking during the development stage of the Galileo Project which is due to enter operational service during the period 2008-2010.
The general results of the GALILEO project:
Determining precise location depends on accurately measuring the distances between receiver and satellite, and that depends on very accurate measurement of the radio signal’s travel time from the satellite to the receiver. As these signals travel at the speed of light, the journey times are tiny fractions of a second.
The receiver measures travel times by comparing ‘time marks’ imprinted on the satellite signals with the time recorded on the receiver’s clock. The time marks are controlled by a highly accurate atomic clock on board each satellite.
These clocks, however, are too expensive to incorporate into standard receivers, which have to make do with small quartz oscillators like those found in a wristwatch. Quartz oscillators are very accurate when measuring times of less than a few seconds, but rather inaccurate over longer periods. The solution is to re-set the receiver’s time to the satellite’s time continuously. This is done by the receiver’s processor using an approximation method involving signals from at least four satellites.
For this system of measurement to work, all satellites need to be synchronised so that they can start transmitting their signals at precisely the same time. This is achieved by continuously synchronising all on-board atomic clocks with a master clock on the ground. These super-accurate clocks have an accuracy equivalent to one second in three million years.
The UIC participation in the project is ensured by organization of conferences and workshops. The presentations from these actions you can see here: