QZS-1 Yaw Attitude Estimation Based on Measurements from the CONGO Network

The first satellite of Japan's Quasi-Zenith Satellite System transmits C/A code and the SAIF signal from different antennas. The baseline vector between these antennas can be computed from differential measurements if the satellite's attitude is known. Based on this vector, the yaw attitude of the spacecraft can be computed. This feature is interesting since the yaw attitude of QZSS satellites is switched between two modes and can be non-nominal during certain time periods. Precise knowledge of the satellite's attitude is essential when processing carrier-phase measurements or satellite laser ranging measurements. This paper introduces the algorithm for baseline vector and yaw attitude estimation and presents results based on real measurements of the CONGO network. The observability of the baseline vector and the accuracy of the yaw angle estimates are discussed. The analysis shows a switch from yaw-steering to orbit-normal orientation and changes of the attitude during an orbit maneuver. Copyright (C) 2012 Institute of Navigation.