24TH ESA SYMPOSIUM ON EUROPEAN ROCKET AND BALLOON PROGRAMMES AND RELATED RESEARCH ARES II – Axial Retention Experiment for Propellant Management Devices Sponges

In this paper, the authors present the scientific results of the ARES II experiment, launched on the REXUS 23 sounding rocket in March 2019 [1]. The ARES II experiment was conceived to investigate the behaviour of liquids in “sponge” type PMDs (Propellant Management Device). These devices (Figure 7), composed of radial panels tapering towards their centre to collect liquid at a certain desired position by capillarity, are used in the space propulsion community to guarantee the delivery of bubble-free propellant to the liquid propulsion engines when high reliability is needed. Sponge devices rely on surface tensions to control and deliver fluid to a desired location in microgravity environments. The capillary force is generally negligible with respect to hydrostatic one in gravitational environments. On the contrary in microgravity, where hydrostatic forces related to accelerations are much smaller than on earth, the surface tensions cannot be neglected any more. The behaviour of liquids in sponges subjected to accelerations perpendicular to their axis was investigated in the past by several authors [2][3][4]. The purpose of the ARES II experiment instead is to investigate the behaviour of liquids in sponges subjected to accelerations acting on the axis of the sponge itself. From the beginning of the 1960s surface tension PMDs were known and used in space vehicles. Though, limited general public documentation is available on this subject. In particular, about the liquid behaviour in sponges under axial acceleration, no information is available in the public domain. The purpose of this experiment is to fill this void by putting sponges in microgravity and acquiring images of the fluid distribution. Figure 1: ARES-II on bench test in ZARM, Bremen 1. Design Overview Like in CAESAR [2], the experimental setup is designed to carry four identical sponges, each one filled at a different level. The experimental fill ratios tested are 37%, 50%, 75%, 100%. The sponges are placed in a centrifuge that activated once the experiment reached microgravity to apply axial acceleration to the samples. The sponges were subjected to increasing axial accelerations and the liquid behaviour was recorded. The experimental results are here after compared with numerical simulations. 1.1. Numerical predictions [5] A series of preliminary CFD (Computational fluid dynamics) investigations were performed prior to designing the system to determine key experiment setup