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Galileo: ground control gets its vital components

PTB has supplied an ensemble of caesium clocks and measuring instruments to the ground control centre of the future European satellite navigation system Galileo. The ensemble of commercial atomic clocks – which were thoroughly and comprehensively tested by PTB before being delivered – is part of the Galileo Precise Timing Facility (PTF) in Oberpfaffenhofen which was developed by the Kayser-Threde company; it is supplemented by two hydrogen masers and facilities for time comparisons. The PTF provides the exact time of the Galileo system; this time is the reference time for all systems linked within Galileo – both on ground and in orbit – and with which they are synchronised, for example for the orbit determination of the satellites or to check the time signals sent by the satellites. In principle, the PTF ensures that the Galileo components all use a time which is painstakingly the same – up to many places after the decimal point. The PTF is thus the basis for the utilisation of Galileo satellite signals for position determination.