Active slosh control and damping - Simulation and experiment

Future reignitable cryogenic upper stages perform long ballistic coasting phases in earth orbit. During those coasting phases, the tanks are loaded with liquid propellants and propellant sloshing occurs due to external disturbances or attitude change maneuvers. The sloshing propellant motion induces reaction forces and torques acting on the space vehicle structure, e.g. rocket upper stages. To keep the upper stage at the desired target attitude, the guidance, navigation, and control (GNC) algorithm commands thruster firings to counter the fluid forces. At ArianeGroup (AG), the Final Phase Simulator FiPS aims at simulating the coupling between fluid mechanics, GNC, and rigid body dynamics. To validate the coupling of GNC with linear lateral water sloshing, on ground experiments at the German Aerospace Center's Hexapod sloshing facility were performed. It was demonstrated that the developed control algorithm is able to damp the linear lateral sloshing within 4 s. FiPS simulations of the open and closed loop sloshing experiments showed that the experimental forces are matched with an uncertainty of less then 5% for open loop phases. For closed-loop phases the simulations match the experimental damping intervals with an accuracy of better than 5% and the force amplitude with an accuracy of about 20%.