Granular mechanics in low gravity: how to land and move on the surface of an asteroid

Small-bodies, such as asteroids, comets, and moons, can be covered by a layer of loose grains, referred to as regolith. The shape and size distribution of the grains can vary drastically from body to body, and the material properties of the grains are often unknown. This complex surface material, coupled with low-gravity, makes it difficult to understand the macroscopic behavior of regolith on small bodies, not to mention its seemingly unpredictable influence on robotic space systems. For example, the NASA OSIRIS-REx sampling mechanism met little resistance when it touched down on the surface of asteroid Bennu. In contrast, the MASCOT rover, deployed by the JAXA Hayabusa2 spacecraft, rebounded several times on the surface of asteroid Ryugu. In this talk, we will discuss how granular materials behave differently under terrestrial and low-gravity conditions. I will present results from drop-tower experiments and Discrete Element Method simulations to show how landing and locomotion depends on gravity, and I will compare the results to existing terramechanics and granular collision models. Finally, I will discuss the implications of our findings within the context of several upcoming small-body missions.

Dr. Cecily Sunday (University of Maryland, Department of Aerospace Engineering, Planetary Surfaces and Spacecraft Lab)