In recent years, the utilization of space has expanded rapidly across communications and broadcasting, positioning, meteorological observation, and remote sensing, resulting in a sharply increasing demand. Under these circumstances, the number of satellites has surged, elevating the risk of collisions and raising concerns about the growing amount of space debris generated by such collisions. Satellites use liquid propellants for orbital insertion and attitude control, but they reach the end of their operational life when propellant is depleted. Many satellites remain in orbit for extended periods after the end of life, and the need to launch replacement satellites further increases the number of objects in orbit, contributing to the growth of space debris. Conversely, if on-orbit propellant refilling can be realized, it may be possible to extend satellite lifetimes and thereby suppress both the need for replacement launches and the associated increase in space debris.

The ultimate goal of the present study is to establish on-orbit propellant resupply technology, and the objective of this work is to develop in-tank gas–liquid separation techniques during propellant transfer under microgravity conditions, which constitute one of the core enabling technologies for achieving that goal. As the first step in the development of this technology, the behavior of liquid in a small, spherical mock-up tank equipped with a vane-type propellant acquisition mechanism utilizing surface tension was observed during filling with simulated propellant under short-duration microgravity conditions generated using a drop tower. Additionally, a variant of the vane-type propellant acquisition mechanism, with baffles added to the central and top sections of the support rods that install the vanes, was also fabricated and tested. It was found that the gas–liquid separation performance of the configuration with top-mounted baffles was superior to that of the other designs.