A combined attitude and sun tracking system for spacecraft using fuzzy logic control

Many spacecraft attitude control systems today use reaction wheels to deliver precise torques to achieve a three-axis attitude stabilization. Despite the extensive studies in attitude controllers, failures still can occur in a spacecraft system. For example, if a spacecraft suffers multiple reaction wheel failure, external disturbances will cause the spacecraft to tumble and lose its ability to correct the attitude error. If the failure is irrecoverable, it may cause the spacecraft to spin uncontrollably and jeopardize the space mission. The most common way to recover a tumbling spacecraft is by firing chemical thrusters sequentially to generate a torque, which can control the total momentum of the spacecraft. Since the thrusters expel reaction mass to produce a torque, this leads to increased fuel consumption and eventually shortened operational life. Most spacecraft have their solar arrays mounted on the y-axis and oriented perpendicular to the sun to receive the maximum amount of solar energy. The solar arrays are rotated using Solar Array Drive Assemblies to track the sun. As a result of the rotations of the solar arrays, internal torques are generated. The main objective in this research is to design a combined attitude and sun tracking system (CASTS) that can utilize the internal torques produced by the solar arrays for attitude control while tracking the sun simultaneously. Two mechanisms are proposed for the CASTS to generate the internal control torque by rotating the solar arrays at different angular speeds. In order to counteract the external disturbance torque, several non-fuzzy logic and fuzzy logic controllers are designed for CASTS. The performance of the proposed CASTS control strategy is tested through numerical simulations. The findings show that all fuzzy logic-based control schemes are able to achieve smaller pitch angle errors compared to the non-fuzzy logic controllers. Overall, the research results show that the proposed CASTS control strategy is effective for controlling the spacecraft attitude and tracking the sun simultaneously.

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