An efficient momentum dumping method for near equatorial orbit satellites

In this research, the improvement of the reaction wheel angular momentum dumping efficiency for a near equatorial orbit satellite through a new Sun-pointing strategy will be presented. Reaction wheels suffer from angular momentum saturation (i.e. when the speed of the reaction wheel reaches its maximum value). However, an alternative set of actuators such as magnetic torquers can be used to prevent such a saturation. It was identified that the torque produced by the magnetic torquers is limited to a plane that is only perpendicular to the geomagnetic field across the satellite body frame. Nevertheless, if the orbit inclination angle with respect to the geomagnetic equator is large, the magnetic field vector periodically changes its direction with respect to the Earth’s inertial reference frame. As a result, on average over the orbital period, the magnetic torques can be applied in all directions within a desired time period. On the other hand, the Earth magnetic field vector for satellites in the near equatorial orbit (NEO) is at a much lower variation. This results in the satellite to lose its three-axis stabilization capability. Consider VELOX-II which is a near equatorial orbit satellite, there was a need to increase the momentum dumping efficiency to improve the reliability and performance of its attitude control system. The proposed new Sun-pointing strategy aligns both the solar panel of the satellite towards the Sun as well as a secondary body frame vector with the Earth’s geomagnetic field vector. To describe the kinematics needed for the proposed method, a cost function was derived using QUEST (QUaternion ESTimation) method to obtain the error quaternion for re-orientation of the satellite. To produce an optimal control torque for re-orientation, a model predictive control (MPC) algorithm has been formulated. The performance of the controller was analysed for varying MPC control parameters (i.e. prediction horizon and control horizon). The produced torque re-orientates the satellite while overcoming the disturbance torque produced by the magnetic torquer for momentum dumping of the reaction wheels. To analyse the momentum dumping performance of the proposed method, the simulation results will be compared with the typical Sun-pointing strategy commonly employed by near equatorial orbit satellites. Results have demonstrated that the proposed method leads to a higher momentum dumping efficiency. Moreover, results have also shown that the proposed method outperforms the conventional method across all seasons and orbit inclination angles. Using an in-house designed hardware-in-the-loop spacecraft attitude control simulator, the new control algorithm has been validated experimentally.Master of Engineerin