Attitude Control of a 2-wheel Satellite by Using a Time-State Control Form

Abstract

The attitude of a satellite is usually controlled by more than 3 reaction wheels. However, to prepare an accident of these wheels, it is important to consider the attitude control by 2 wheels. Especially, when the initial angular momentum of the system is not zero, the system has a drift term and it is impossible to control to arbitrary attitude. Therefore, the purpose of this research is to control the direction of a satellite's communication antenna to the target direction. To achieve this purpose, we introduce an idea of equal ratio divergence with Rodrigues parameters. This idea is based on the feature of Rodrigues parameters: By diverging Rodrigues parameters with keeping some ratio, the attitude converges to specified value corresponding to the ratio. To use this feature,we transform the system into a time-state control form. By stabilizing a time-state control form, the antenna achieves the target conditions. Moreover, controllable attitudes become clear by analyzing this method. In addition, proposed method can also works to control the attitude arbitrarily when the angular momentum is zero. Note that this method can be used only when one of the wheel is set along the antenna.