Development of guidance algorithms for attitude maneuvers of small satellites

One of the most essential tasks of a satellite is to point an instrument along a desired direction in order to achieve mission requirements. In many cases, this operation is complicated due to the presence of sensitive on-board instruments, which cannot be pointed along certain directions, such as the Sun or other bright objects. This problem can be analyzed as a reorientation problem in the presence of attitude constraints. In literature there are not many research papers that address the constraints problem, and its solution has great importance for practical scientific missions. In this thesis work, a guidance algorithm based on the Artificial Potential Field method is analyzed and implemented in MATLAB/Simulink environment, which allows us to describe the desired pointing and the restricted areas through potential fields. A hybrid attractive potential field centered at the desired pointing has been implemented: parabolic close to the objective and conic far away from it, in order to prevent the reaction wheels from saturating and at the same time have a smoother response; to deal with the restricted areas, a hyperbolic repulsive potential field has been implemented, with extra care in designing the gain so that the reference angular velocity remained compatible with the constraint given by the actuation system. The advantage of this method is its analytical approach which allows us not to have to modify either the controller hardware or software, and therefore suitable for on-board calculation and planning. Satellite kinematics and dynamics are described using unit quaternions to avoid the singularity issue which Euler angles are affected by. By combining the guidance with a sliding mode control algorithm, we obtain an attitude control law that guarantees good performance and robustness, allowing flexibility in the presence of obstacles and orbit perturbations.