Coasting Phase Propellant Management for Upper Stages

The next generation of European cryogenic upper stages, namely the A5ME upper stage, is expected to perform multiple engine restarts in order to enhance the mission flexibility. The management of the propellant in the upper stage tanks under g conditions is thus a major issue with respect to the handling of these phases. A number of different tasks play a major role, e.g. the coupling of the rigid body motion and the sloshing in the tanks driven by the controller of the stage. Furthermore also thermal aspects are of importance which have to be considered. Coasting phases are not a new aspect with respect to mission scenarios of upper stages as they occur during every P/L release. Main difference in case of a restart mission is however that the tank fill level is much higher compared to past P/L separations with a nearly empty tank. The coupling between rigid body motion, controller and fluid motion is thus much stronger. Astrium therefore developed a software tool, called "FIPS", which is able evaluate the coupled closed loop rigid body motion including fluid dynamics and the control algorithm. The tool couples the high sophisticated CFD software FLOW-3D with an Astrium developed closed loop rigid body dynamics simulator. The presentation discusses details concerning the propellant behaviour in coasting phases. The impact of internal equipments such as sloshing baffles will be detailed. One conclusion of the assessment is that to a major part disturbing torques are non-negligible such that a realistic propellant behaviour can only be realized in a closed loop simulation. The impact of the upper stage controller can not be neglected.