Yaw attitudes for BDS-3 IGSO and MEO satellites: estimation, validation and modeling with inter-satellite link observations

Abstract: The disclosed satellite metadata as well as previous estimations using Revise Kinematic Precise Point Positioning (RKPPP) approach with L-band data have already demonstrated the continuous yaw steering model used by BDS-3 Medium Earth Orbit (MEO) satellites manufactured by China Academy of Space Technology (CAST) in deep eclipse seasons instead of the orbit normal mode. However, the yaw model has not been validated for MEO satellites manufactured by Shanghai Engineering Center of Microsatellites (SECM), as the horizontal phase center offsets (PCO) approaches zeros, similar for BDS-3 Inclined Geostationary Orbit (IGSO) satellites. In this study, the inter-satellite link (ISL) data were used to estimate the yaw angles of BDS-3 IGSO and MEO satellites with accuracy of around 1.49{\deg} to investigate their yaw behaviors, particularly in the deep eclipse seasons. The estimates confirm that the IGSO and MEO satellites from CAST show the similar yaw behaviors, while the SECM MEO satellites do not fully comply with the attitude law published by China Satellite Navigation Office (CSNO). The attitude transition postpones from that predicted by CSNO yaw law, and occurs when the yaw angle is less than 5{\deg} and the elevation angle of the Sun above the orbital plane (beta angle) crosses 0{\deg}. The transition completes within three minutes with a rate about 0.055{\deg}/s. A model is proposed to predict these behaviors, and the ISL residuals return to normal levels, and became more stable in the adjacent of midnight and noon points. Once the yaw models are used.