Attitude stabilization of a flexible spacecraft using combined PZT/optical sensors

The problem of stabilizing the time delayed control of a flexible space structure is analyzed in this paper. A free floating platform is used to investigate the space multibody dynamics and control. A first necessary step to develop stabilizing techniques is considered the availability of a set of measurements as complete as possible: in particular measurements of the elastic vibrations are necessary in addition to classic attitude measurements. At the scope, a net of PZT sensors have been designed and manufactured on a composite material panel, purposely built to resemble a space structure. A combined use of the PZT/optical sensor is proposed, where the role of the camera is to estimate the PZT parameters that can be changed after the manufacturing or for environmental aging. When this calibration process is performed, PZT can be used as standalone sensors for measuring also the elastic displacement of the structure. Once these measurements of attitude and elastic displacement are obtained, two stabilizing techniques have been developed, the Finite Spectrum Analysis, already known in literature, and the newly developed High Fidelity Filter approach, based on the design of a Kalman filter with large confidence on the process dynamics. It is shown that both techniques manages to increase the delay margin of the system, thus obtaining a stable maneuver, but the second approach reach this goal with very low residual vibrations and a remarkable fuel saving.