Resonance Mitigation in the Attitude Control of a Flexible Large Solar Sail

Abstract: This project is about the design process of a resonancemitigating algorithm for a large solar sail. The solar sail isa structure made up by four long booms in a cross patternwith suspended sails between the edges of the booms. Thespacecraft in this report is controlled using smaller rotatingsails at each tip of the booms. Since the booms are longthey will experience significant bending moment even thoughthe actual force from the control sails will be small. Thisbending has a high risk of exciting the spacecraft’s resonancemodes, which will in turn complicate the control of theentire spacecraft. Because of this it is necessary to designan algorithm to mitigate resonance excitation. To design thisalgorithm three main steps were taken, an approximation ofspacecraft resonance modes, a valid mathematical model ofthe system and robustness building to handle model error.The resonance modes were approximated through analyticalformulas. The boom model was determined by combiningdifferent approaches from previous similar works. Finally,the controller chosen was a simple PID controller with abuilt-in saturation limiter to make sure the controller stayswithin the spacecraft’s operating bounds. To ensure robustness,multiple test simulations were made on systems with differentresonance modes compared to the true system. The chosencontroller passed these tests. Ultimately the chosen controllerreduced the settling time of the resonance oscillations by 75%.