Study and integration of a hybrid attitude control system for nanosatellites in Low Earth Orbit

This thesis presents the development and implementation of the Attitude Determination and Control System (ADCS) for the 3cat-8 satellite, a project undertaken by the UPC NanoSat Lab. The ADCS is essential for maintaining the desired orientation of the satellite, which is crucial for performing scientific experiments, gathering solar power and communicating with the ground station. This work primarily focuses on the complete modeling of a satellite using a hybrid Magnetorquer + Reaction wheel actuator scheme, and the control algorithms that needed to obtain and maintain a desired orientation during flight. Various options for representing attitude in space are explored, with quaternions chosen as the basis for the attitude determination and control algorithms. Space dynamics are also thoroughly examined in order to create the backbone for a simulation software with which the control laws will be tested and validated. To ensure that the simulation environment closely mirrors reality, state-of-the-art environmental models of the Earth are studied and implemented. Additionally, the disturbances acting upon the satellite are deeply analyzed and characterized, employing numerical and statistical methods to obtain accurate yet computationally efficient implementations of said disturbances. The actuation scheme has been found to impact the control algorithms used for attitude control in the pointing modes, creating the need for allocating the control commands across the actuator suite, as well as unloading the angular momentum stored in the reaction wheel. The final satellite model and the selected control laws have been tested in the simulated environment, demonstrating their correct functioning and mostly fulfilling the operational requirements initially set for the 3cat-8 satellite. The thesis concludes with suggestions for possible improvements in the attitude control scheme and recommendations for future work.