Time metrology in the Galileo navigation system: The experience of the Italian National Metrology Institute

Timekeeping is crucial in Global Navigation Satellite Systems (GNSS), being the positioning accuracy directly related to a time measurement. As a consequence, the typical expertise of time metrology laboratories is necessary in many different aspects of a navigation system. This paper presents the experience of INRIM in the development of the Galileo navigation system from the earlier studies till the very recent In Orbit Validation phase showing how the time metrology practice has been useful in the understanding of time aspects of navigation and showing as well how the navigation service perspective has stimulated new ideas and better understanding of time measures.