Effect of Reduced-Gravity Conditions on the Flowability of Granular Media

We present a study on investigation of fundamental properties of granular media as gravity levels are reduced. Probes and rovers are sent to different solar-system bodies encountering surfaces covered with granular materials. Questions of how deep probes sink in or how well rovers can drive on such surfaces can only be answered if the fundamental properties of the granular material and its behaviour under reduced gravity conditions are known. We are interested in the static and dynamic characteristics and especially at which lower boundary in g-level particles become dominated by cohesive forces. The experiments were performed in the Bremen Drop Tower facility using the microgravity environment so that a substitute `gravity' field could be applied via a rotating centrifuge. The rotation rate could be varied to adjust for different acceleration levels. Surface flow effects were simulated in two flat (quasi-2D) sandglass experiments, in a rotating tumbler and in an avalanche box. We will present results from 15 microgravity experiments in an acceleration range between 0.01g and 1g.