Phd in AERONAUTICS AND SPACE ENGINEERING

Thesis title: CONTROL-ORIENTED MODELLING OF AN INTEGRATED ATTITUDE AND VIBRATION SUPPRESSION ARCHITECTURE FOR LARGE SPACE STRUCTURES

The thesis focuses mainly on the problem of active vibration suppression for a spacecraft equipped with very large flexible structures. In particular, this research aims at proposing an end-to-end general architecture for an integrated attitude-vibration control system, starting from the design of structural models to the synthesis of the control laws. In detail, large space structures based on realistic missions (as the first Large European Antenna (LEA), NASA's SWOT) are investigated as study cases, in accordance with the tendency of increasing the size of the scientific instruments to improve their performance and sensitivity, being the drawback an increase of its overall flexibility. An active control method is therefore required to guarantee satisfactory pointing and maximum deformation by avoiding classical stiffening methods. Therefore, the instrument is designed to be supported by an active deployable frame hosting an optimal minimum set of collocated smart actuators and sensors. Different spatial configurations for the placement of the distributed network of active devices are investigated, both at closed-loop and open-loop levels. Concerning closed-loop techniques, a method to optimally place the poles of the system when considering a Direct Velocity Feedback (DVF) controller is proposed to identify simoultaneusoly the location and number of active devices for vibration control with an in-cascade optimization technique. Then, two general and computationally efficient open-loop placement techniques, namely Gramian and Modal Strain Energy (MSE)-based methods, are adopted as opposed to heuristic algorithms, which imply high computational costs and are generally not suitable for high-dimensional systems, to propose a placement architecture for generically shaped tiridimensional space structures. Then, an integrated robust control architecture for the spacecraft is presented as composed of both an attitude control scheme and a vibration control system. To conclude the study, attitude manoeuvres are performed to excite main flexible modes and prove the efficacy of both attitude and vibration control architectures. Moreover, a second part of this research is dedicated to address the problem of improving autonomy and self-awarness of modern spacecraft, by using machine-learning based techniques to carry out Failure Identification for large space structures and improving the pointing performance of spacecraft (both flexible satellite with sloshing models and small rigid platoforms) when performing repetitive Earth Observation manoeuvres.