Discoid and Asymmetrical Micro-Satellite Propulsion Mode Attitude Control with Great Mass Change and without Angular Rate Sensor

Abstract

The center of mass of the micro-satellite can offset due to fuel consumption in the course of propulsion, with the interference of external orbital environment such as gravity gradient torque and solar radiation torque. If the structural shape is discoid and asymmetrical, the attitude control may be difficult. The only solution is to design a robust controller, so that the attitude pointing of the satellite can meet the mission requirements with the interference of internal parameter perturbation and external disturbance. This study applied the robust control theory control law in the design of Formosat-3 propulsion mode attitude control, and carried out cross validation of the feasibility of the controller by time domain and frequency domain stability analyses. This study used controller as the experimental result. The time domain performance indexes (e.g., rise time, maximum overshoot and stabilization time) of the designed controller were consistent with the robust stability margin of stable performance index of frequency domain. Meanwhile, in order to reduce the weight and manufacturing cost of satellite, in the design of satellite attitude angular rate determination, the project used unscented kalman filter (UKF) algorithm, coarse sun sensor (CSS) and earth horizon sensor (EHS) as measurement components to obtain the satellite attitude without rate gyro. The research method and procedures in this study are applicable to any shaped and asymmetrical satellites with large mass variation and without angular rate sensor. The attitude sensors include three-axis magnetometer, horizon sensor, CSS as the analytic platform for stability of attitude control.