The spacecraft Attitude Control System (ACS) performance and robustness depend on the interaction effects between the fuel slosh motion, the panel's flexible motion and the spacecraft rigid motion, mainly during translational and/or rotational maneuvers. In regards to satellite pointing accuracy flexibility and fuel slosh are the two most important effects that should be considered in the satellite ACS design since their interactions can damage the ACS performance and robustness. Once, the

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... t vibration frequencies, normally of the slosh mode are about six times less than of the ACS bandwidth. Therefore, there is a strong possibility that this mode can destabilize the ACS pointing. This phenomenon is called spillover, because the control effort spills over outside the control bandwidth. As a result, the designer needs to explore the limits between the conflicting requirements of performance, that is, increase of the bandwidth without introduction noise in the ACS keeping the system robustness to parameters variation. In this paper one applies the H infinity control method which is able to deal with these two design requirements (performance and robustness) considering the controller error pointing that may be limited by the minimum time necessary to suppress disturbances that affects the satellite attitude acquisition. The equations of motions are obtained considering Lagrange method for small flexible deformations and a mechanical model of liquid sloshing which allows modeling and investigating the longitudinal dynamic characteristics of partially filled liquid tank during a pitch maneuver. The results of the simulations have shown that the H-infinity controller was able to control the rigid motion and suppress the vibrations