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

Abstract

The first satellite of Japan’s Quasi-Zenith Satellite System (QZSS) has been launched in September 2010, and its signal transmission has been activated at the end of the same year. The satellite transmits five signals from its L-band main antenna, including C/A code and L1C on L1, and the SAIF signal from a dedicated antenna mounted with an offset to the main antenna. Using differential pseudorange and carrier-phase measurements, it is possible to compute the phase center offset vector, or baseline vector, between these two antennas, if the satellite’s attitude is known. Using this vector as a priori information, it is furthermore possible to compute the yaw attitude of the spacecraft. This is a unique feature of the QZSS satellites and particularly interesting since their attitude mode is switched between yaw-steering and orbit-normal orientation during certain periods. Precise knowledge and consistent modeling 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 collected with five QZSS-capable receivers of the CONGO network. The observability of the baseline vector and the accuracy of the yaw angle estimates are discussed. The analysis for the yaw attitude estimation includes a switch from yaw-steering to orbit-normal orientation as well as changes of the attitude mode during an orbit maintenance maneuver.