Attitude control of bias momentum micro satellite using magnetic and gravity gradient torque

Earth pointing satellites commonly use bias momentum for attitude control. It provides gyroscopic stability against the external disturbance torque. Typically, the bias momentum satellite use momentum wheel and thruster for actuator and star tracker or pairs of horizon and a sun sensor to determine the direction of angular momentum. This paper proposes an effective technique to control the angular momentum of Lapan-Tubsat satellite using wheels and magnetic coil for actuator and overcome the limitations of the spacecraft that has no on-board horizon sensor and magnetometer that usually used to measure the magnetic field. The determination of angular momentum direction use video camera instead a horizon sensor even though it is available once per 24 hours of ground station contact. This idea is effective if only the disturbance torque and the angular momentum has been characterized and established. After the video camera gives attitude information the satellite operator tries to control the direction of angular momentum by over or under-compensate the disturbance torque using magnetic coil. On Lapan-Tubsat, the disturbance torque level is in the order of 10^-5 Nm, i.e. 10% of the maximum coil torque.