http://arxiv.org/abs/2011.12890
The surfaces of many planetary bodies, including asteroids and small moons, are covered with dust to pebble-sized grains held weakly to the surface by gravity and contact forces. The Hayabusa2 and OSIRIS-REx missions have both confirmed that this is the case for the asteroids (162173) Ryugu and (101955) Bennu, respectively, raising the question of how surface disturbances propagate in low-gravity environments. Instruments including sensors and anchoring mechanisms for use on such surfaces will require efficient and effective design principles. We analyze the behavior of a flexible probe inserted into loose regolith as a function of speed and gravitational acceleration as a prototypical example exploring the relevant dynamics. The EMPANADA experiment (Ejecta-Minimizing Protocols for Applications Needing Anchoring or Digging on Asteroids) flew on several parabolic flights. It employs a classic granular physics technique, photoelasticity, to quantify the dynamics of a flexible probe during its insertion into a laboratory system of bi-disperse, cm-sized model grains. We identify the grain-scale forces throughout the system for probe insertion at a variety of speeds and for four different levels of gravity: terrestrial, martian, lunar, and microgravity. We demonstrate that the photoelastic techniques provide results that complement traditional load cell measurements, with both methods identifying discrete, stick-slip failure events that increase in both magnitude and frequency as a function of the gravitational acceleration. For microgravity experiments, stick-slip behaviors are negligible. We additionally find that faster probe insertion can suppress stick-slip behaviors where they are present. We conclude that the behavior of regolith on rubble pile asteroids is likely quite distinct from the environments found on larger objects.
J. Featherstone, R. Bullard, T. Emm, et. al.
Thu, 26 Nov 20
19/65
Comments: N/A