Time Comparison Experiments Between the QZS-1 and its Time Management Station

The National Institute of Information and Communications Technology (NICT) developed the time management system of the first Quasi-Zenith Satellite (QZS-1) in order to monitor the onboard clock as a part of the satellite navigation system. While an onboard clock is usually estimated together with the orbit of the satellite, the system described here enables the direct measurement of an onboard clock by comparing it with a ground clock by making use of a two-way time and frequency transfer which removes most of the propagation errors. Our system achieves a measurement precision of about 25 picoseconds which is an order of magnitude better than the precision of the clock parameters obtained from the combined orbit and clock estimation. Copyright © 2013 Institute of Navigation