Simulating Regoliths in a Microgravity Environment

Review of Scientific Instruments, 2018

A new experimental facility has been designed and constructed to study driven granular media in a low-gravity environment. This versatile instrument, fully automatized, with a modular design based on several interchangeable experimental cells, allows us to investigate research topics ranging from dilute to dense regimes of granular media such as granular gas, segregation, convection, sound propagation, jamming, and rheology—all without the disturbance by gravitational stresses active on Earth. Here, we present the main parameters, protocols, and performance characteristics of the instrument. The current scientific objectives are then briefly described and, as a proof of concept, some first selected results obtained in low gravity during parabolic flight campaigns are presented.

Physics of Fluids, 2006

We employ discrete element three-dimensional simulations that include realistic modeling of physical system boundaries to determine the influence of gravity on velocity profiles and stresses for frictional inelastic particles that are confined in an angular Couette cell, and sheared by a rotated upper wall. In addition to Earth gravity, we consider other gravitational fields, in particular those of the Moon and Mars. The computational techniques are based on hard-sphere simulations of polydisperse particles at relatively high volume fraction (50-55%). We find that the presence of gravity induces significant changes of the velocity profiles and stresses. One important nondimensional parameter in the problem is shown to be IΩ=γ˙d/Pg/ρs, where γ˙ is the imposed shear rate, Pg is the weight of the system per unit area due to gravity, and ρs is the solid density. We also consider systems that are vibrated in addition to being sheared, since vibrations are one of several important methods for agitating (e.g., fluidizing and/or unjamming) granular systems. We find that the introduction of nondimensional acceleration Γ=a(2πf)2/g, where a,f,g are the amplitude and frequency of oscillations, and the acceleration of gravity, explains novel features that develop in these complex granular systems.

EPJ Web of Conferences

The surfaces of many planetary bodies, including asteroids, moons, and planets, are composed of rubble-like grains held together by varying levels of gravitational attraction and cohesive forces. Future instrumentation for operation on, and interacting with, such surfaces will require efficient and effective design principles and methods of testing. Here we present results from the EMPANADA experiment (Ejecta-Minimizing Protocols for Applications Needing Anchoring or Digging on Asteroids) which flew on several reduced gravity parabolic flights. EMPANADA studies the effects of the insertion of a flexible probe into a granular medium as a function of ambient gravity. This is done for an idealized 2D system as well as a more realistic 3D sample. To quantify the dynamics inside the 2D granular material we employ photoelasticity to identify the grain-scale forces throughout the system, while in 3D experiments we use simulated regolith. Experiments were conducted at three different levels...

Physics of Fluids, 2005

We report the results of three-dimensional molecular dynamics simulations of sheared granular system in a Couette geometry. 1 The simulations use realistic boundary conditions that may be expected in physical experiments. For a range of boundary properties we report velocity and density profiles, as well as forces on the boundaries. In particular, we find that the results for the velocity profiles throughout the shearing cell depend strongly on the interaction of the system particles with the physical boundaries. Even frictional boundaries can allow for significant slippage of the particles, therefore, reducing the shear in the system. Next, we present shear rate dependence of stress, including mean force and force fluctuations, both for controlled volume, and for controlled stress configurations. We discuss the dependence of solid volume fraction on shear rate under the constant pressure condition, and Bagnold scaling in volume controlled experiments. In addition, we study the influence of oscillatory driving on the system properties. * oleh.baran@njit.edu; http://math.njit.edu/~oleh/ 1 Movies of the simulations can be found at

2021

The surfaces of many planetary bodies, including asteroids and small moons, are covered with dust to pebble-sized regolith held weakly to the surface by gravity and contact forces. Understanding the reaction of regolith to an external perturbation will allow for instruments including sensors and anchoring mechanisms for use on such surfaces to implement optimized design principles. We analyze the behavior of a flexible probe inserted into loose regolith simulant as a function of probe speed and ambient gravitational acceleration to explore 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 system of bi-disperse, cm-sized model grains. We identify the grain-scale forces throughout the system for probe insertion at a variety of sp...

arXiv: Earth and Planetary Astrophysics, 2020

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 du...

Physical Review E, 2011

The response of an oscillating granular damper to an initial perturbation is studied using experiments performed in microgravity and granular dynamics simulations. High-speed video and image processing techniques are used to extract experimental data. An inelastic hard sphere model is developed to perform simulations and the results are in excellent agreement with the experiments. The granular damper behaves like a frictional damper and a linear decay of the amplitude is observed. This is true even for the simulation model, where friction forces are absent. A simple expression is developed which predicts the optimal damping conditions for a given amplitude and is independent of the oscillation frequency and particle inelasticities.

The Planetary Science Journal, 2021

The surfaces of many planetary bodies, including asteroids and small moons, are covered with dust to pebble-sized regolith held weakly to the surface by gravity and contact forces. Understanding the reaction of regolith to an external perturbation will allow for instruments, including sensors and anchoring mechanisms for use on such surfaces, to implement optimized design principles. We analyze the behavior of a flexible probe inserted into loose regolith simulant as a function of probe speed and ambient gravitational acceleration to explore 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 system of bi-disperse, centimeter-sized model grains. We identify the force chain structure throughout the system during probe insertion at...

2014

The European Space Agency's ROSETTA spacecraft, en route towards its target Comet 67P/Churyumov-Gerasimenko, passed by the Asteroid (21) Lutetia on the 10 July 2010 at a distance of 3170km.OSIRIS - the Optical, Spectroscopic, and Infrared Remote Imaging System on board Rosetta - took 462 images. These images show that (21) Lutetia is covered with a thick layer of regolith. On slopes of several craters this regolith layer collapsed in landslide-like events. A possible trigger mechanism for these low-gravity avalanches is the slow impact of a small mm to cm-sized body. An experiment was conducted to investigate if such an impact is a viably mechanism to trigger an avalanche on an asteroid. The data collected during the experimental investigation show that these minor impacts can trigger a landslide-like event if the target material is tilted close to the angle of repose. The grain size distribution also influences the likelihood of an avalanche depending on the type of material un...