Probe-insertion exhibits gravity-dependent stick-slip dynamics in experiments on a model system for regolith surfaces. (arXiv:2011.12890v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Featherstone_J/0/1/0/all/0/1">Jack Featherstone</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bullard_R/0/1/0/all/0/1">Robert Bullard</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Emm_T/0/1/0/all/0/1">Tristan Emm</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jackson_A/0/1/0/all/0/1">Anna Jackson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Reid_R/0/1/0/all/0/1">Riley Reid</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shefferman_S/0/1/0/all/0/1">Sean Shefferman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dove_A/0/1/0/all/0/1">Adrienne Dove</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Colwell_J/0/1/0/all/0/1">Joshua Colwell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kollmer_J/0/1/0/all/0/1">Jonathan E. Kollmer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Daniels_K/0/1/0/all/0/1">Karen E. Daniels</a>
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.
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.
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