Ricerc@Sapienza

Many future space systems will require the presence of very large flexible appendages. Because of the launcher constraints on payload mass, spacecraft structures are lightweight and highly flexible with densely packed modal frequencies and extremely low damping values. Since these structures are subjected to a variety of dynamic perturbations produced by the coupling with attitude maneuvers, transient thermal states, sloshing phenomena and on-board noisy equipment, the lightly damped nature of these structures can lead to elastic vibrations in a broad frequency spectrum producing unwanted noise to sensitive instrumentations.
Current state-of-the-art for missions with large appendages are solved at AOCS (Attitude Orbit Control System) level by designing controllers with very low control bandwidths or limited input commands in order to minimize the impact of flexible modes on spacecraft dynamics. With the new strict requirements envisioned for pointing and shape accuracy of next generation missions and the novel space architectures in development, the aforementioned problems pose multiple challenges for current control architectures; furthermore, the AOCS design for such complex system encounters an ulterior significant difficulty which is the presence of uncertainties on several vehicle parameters.
In this context, the proposed study investigates the application of advanced control methods for combining satellite AOCS with vibration control of the appendages via a network of smart devices in the unified framework of Linear Fraction Transformation (LFT) and Structured Singular Value (s.s.v). In practice, an uncertain state space plant is extrapolated from the 3D structural model developed in a commercial FEM software together with transducers dynamics. Because of the size of the state space model and the huge number of parametric uncertainties rather novel techniques will be used to generate a suitable LFT model to be handled by robust control optimization algorithms.