Comparison of Different Magnetorquer Control Laws for QSAT

Abstract

This paper explains the attitude control method for a 50 kg class satellite QSAT. It uses three-axis magnetorquers for control and a gravity-gradient extension boom for enhancement of the attitude stabilization. We divide the mission period into three main attitude-control phases. The first phase refers to the de-tumbling which ends when one particular satellite axis is roughly along the local Earth-pointing direction. In the second phase, we extend the boom. The third phase refers to the normal mission mode, when accurate attitude control will be achieved by means of the magnetorquers. We construct a number of normal-mode control algorithms and evaluate their performances by simulations. We calculate the required control torque by the PD (Proportional-Derivative) control method. The differences of the methods appear in the calculations of the required magnetic moments. In this paper, we simulate the following methods; 1) simplified linearized dynamics equation method, 2) the LQR (Linear Quadratic Regulator) method, and 3) the cross product method which utilizes only data from the magnetometer and the rate gyros. From the simulations, we conclude that "simplified linearized dynamics equation method" is the most efficient method for QSAT.