Nowadays, the success of space activities and exploration missions is conditioned by the operation of a spacecraft in compliance with the mission specifications. In particular, the operating conditions are strongly influenced by the technology implementing the management of the conventional and cryogenic propellants. In the case of the upper stages of launchers and satellites, the tank with its ancillary systems is the central equipment, involved in complex propellant handling operations performed in various phases of the mission. Consequently, the design process relies on the understanding of the propellant’s behaviour inside the tank, which requires knowledge about the propellant position, its time evolving topology and thermodynamic state.