ESA GNC Conference Papers Repository

The FORMOSAT-5 (FS-5) is the fifth space program initiated in 2008 by National Space Organization (NSPO) within National Applied Research Laboratories (NARL) in Taiwan, Republic of China (ROC). The FS-5 Satellite is a three-axis attitude stabilized spacecraft providing high precision attitude determination and control for a high resolution Remote Sensing Instrument (RSI) during nominal operations. To meet the 0.012 deg, 3-sigma, per axis, absolute attitude knowledge requirement flown-down from RSI for its geo-location accuracy, the micro-Advanced Stellar Compass (uASC) consisting of three Camera Head Units (CHUs) is mounted on a stable optical bench common to the RSI structure. The uASC is a highly advanced and fully autonomous star tracker designed, developed, and produced by the Measurement & Instrument System (MIS) Section of the Ørsted Department of the Technical University of Denmark (DTU). The attitude data in term of quaternion provided by the three CHUs will be fused or combined in real time to obtain the optimal attitude solution for the Attitude and Orbit Control System (AOCS). The three CHUs are orientated in such a way that during normal imaging operation at least two CHUs will not be intruded by Sun, Earth, or Moon. Nevertheless, attitude glitch due to unknown CHU misalignments with respect to the RSI reference frame may occur while transitioning from three CHUs to two CHUs or vice versa because of bright object intrusions to the CHUs. Special cares need to be incorporated in the attitude data fusion to prevent those glitches. This paper presents a method for implementing a glitch-free data fusion algorithm combining multiple attitude solutions when intrusions occur. Simulation results illustrating the benefit of applying the proposed data fusion algorithm on the RSI geo-location performance will be included in the paper.