Clocks in Space: Precision Timing for Satellite Navigation Systems and Fundamental Physics

Satellite navigation systems such as GPS and Galileo determine the user’s position by measuring the time of flight of signals broadcast from satellites.  This transit time is proportional to the distance between the user and each satellite of the constellation.  Since errors in the timing measurements lead directly to an error in the calculated position, it is essential to have precise and stable clocks on board.  I will discuss how clocks based on an atomic reference have become the state-of-the-art in clock development, and also how clocks in space give us the ability to test our understanding of fundamental physics, including Galileo’s concept of the equivalence principle.