Attitude control for momentum biased satellites based on yaw observer

Attitude control problem of a three-axis stabilized, momentum biased, and nadir-pointing satellite is investigated based on yaw observer. Since the measurement of the yaw angle is unavailable by horizon sensor, an attitude control scheme of the satellite is proposed based on yaw observer. The pitch control is attained by the measurement of the pitch angle. The roll/yaw design is composed of two parts; a PD controller based on yaw observer and a wheel decoupling function. The satellite considered is actuated by momentum and reaction wheels. Magnetic torqrods generate magnetic dipole moments whose interaction with the Earth magnetic field can produce magnetic torques necessary to remove the excessive momentum of wheels. Numerical simulation results show that high pointing accuracy is achieved within the range of wheel torques.