Euclid GNC: an optimal attitude estimation algorithm in an output regulation problem framework for the control of a scientific satellite in Fine Pointing Mode

The work presented in this thesis is based on the design and analysis of the control system of the EUCLID satellite in Fine Pointing Mode. Its dynamical behaviour has been reproduced considering the effective errors given by the sensors and the main disturbances affecting its motion during the mission. Through this work it has been designed an algorithm which is capable of providing the software robustness and the reduction of the computational cost needed in the industrial world and at the same time reaching the performance aimed by the academy. In other words, it has been showed that the industrial and the academical worlds can be synthesized in a highly efficient way. This goal has been achieved by designing an optimal estimator, which is capable of correcting the measurements coming from the sensors in terms of noise and delay, coupled with a linear optimal control algorithm fed into an error feedback output regulator. The estimator has been designed on the well-known Multiplicative Extended Kalman Filter model, modified for the delay correction of the star tracker by means of a backward state propagation for the state update correction. Meanwhile, the controller is exploiting the optimal control and the error feedback output regulation theory, leading to the tracking of not only step reference trajectories but also sinusoidal time varying signals. Eventually, the reported simulations are highlighting the high performances reached by the observer, obtaining a very low error on the angular position, order of 10^(-3) deg, and angular velocity estimation, order of 10^(-5) rad/s. Furthermore, the pointing error requirement has been respected thanks to the high accuracy provided by the optimal controller, which gave an angular error of the order of 10^(-3) deg. Lastly, the results obtained by the output regulator showed a remarkable ability in annihilating the tracking errors not only for periodic unstable but also for asymptotically stable reference trajectories.