SPACECRAFT ATTITUDE ESTIMATION USING UNSCENTED KALMAN FILTERS, REGULARIZED PARTICLE FILTER AND EXTENDED H∞ FILTER

In this work, the attitude determination and the gyros drift estimation will be described for nonlinear systems using the Extended Kalman Filter (EKF), Extended H-infinity. Filter (EH infinity F), Second-Order Extended H-infinity Filter (SOEH infinity F), Unscented Kalman Filter (UKF) and Regularized Particle Filter (RPF). An analysis of these estimation methods will be done, verifying which of them present better precision in such study. The attitude model is described by quatemions and the attitude sensors available are two DSS (Digital Sun Sensors), two IRES (Infrared Earth Sensor), and one triad of mechanical gyros. The application uses the simulated measurement data for orbit and attitude of the CBERS-2 (China Brazil Earth Resources Satellite) which has polar sun-synchronous orbit with an altitude of 778km, making about 14 revolutions per day. In this orbit, the satellite crosses the equator line always at the same local time, around 10:30 am. This dynamics allows the same conditions of solar illumination to be obtained during the acquisition of images. The simulated measurements of the CBERS-2 were provided by the inhouse package PROPAT, a Satellite Attitude and Orbit Toolbox for Matlab. The results in this work show that one can reach accuracies in attitude determination within the prescribed requirements, besides providing estimates of the gyro drifts which can be further used to enhance the gyro error model.