An experimental study of low-velocity impacts into granular material in reduced gravity

Murdoch, Naomi; Martinez, Iris Avila; Sunday, Cecily; Zenou, Emmanuel; Cherrier, Olivier; Cadu, A.; Gourinat, Yves

doi:10.1093/mnras/stw3391

Cited by 24 publications

(28 citation statements)

References 43 publications

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“…However, to better replicate an asteroidal environment, reduced-gravity experiments can be performed on the Earth with Atwood machines (Murdoch et al 2017) and parabolic flights (Colwell et al 2008(Colwell et al , 2015. With these methods, environmental gravity as low as 10 −2 g can be achieved.…”

Section: Materials Typementioning

confidence: 99%

Numerical modeling of lander interaction with a low-gravity asteroid regolith surface

Thuillet

Zhang

Michel

et al. 2021

A&A

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Context. The JAXA asteroid sample return mission Hayabusa2 reached its target (162173) Ryugu in June 2018 and released the European (CNES-DLR) lander MASCOT in October 2018. MASCOT successfully landed on the surface, and the Hayabusa2 Optical Navigation Camera system has been able to image parts of the MASCOT trajectory. Aims. This work builds on our previous study of interactions between a landing package and a granular material in the context of MASCOT on Ryugu. The purpose is to expand our knowledge on this topic and to help constrain physical properties of surfaces by considering the actual trajectory of MASCOT and observations of Ryugu from Hayabusa2. Methods. We ran a new campaign of numerical simulations using the N-body code pkdgrav with the soft-sphere discrete element method by expanding the parameter space to characterize the actual landing scenario of MASCOT on Ryugu. The surface was modeled as a granular medium, but we also considered a large boulder in the bed at various depths and a rigid wall representing a cliff. MASCOT was faithfully modeled as the actual lander, and we considered different impact angles, speeds, and surface slopes. We were particularly interested in the outgoing-to-incoming speed ratio of MASCOT during the landing process. Results. We found that a boulder in the bed generally increases both the stochasticity of the outcomes and the speed ratio, with larger increases when the boulder sits closer to the surface. We also found that the surface slope does not affect our previous results and that the impact speed does not affect the speed ratio for moderate-friction granular material. Finally, we found that a speed ratio as low as 0.3, as estimated in the actual scenario, can occur with a solid-rock surface, not only with a soft surface, because the geometry of the lander is nonspherical. This means that we must infer the physical properties of the surface from outcomes such as the speed ratio with caution: it depends on the lander geometry.

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Section: Materials Typementioning

confidence: 99%

Numerical modeling of lander interaction with a low-gravity asteroid regolith surface

Thuillet

Zhang

Michel

et al. 2021

A&A

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“…Laboratory experiments have been developed to study reducedgravity impact dynamics (Colwell & Taylor 1999;Murdoch et al 2017;Brisset et al 2018), avalanching (Kleinhans et al 2011;Hofmann, Sierks & Blum 2017), angle of repose (Nakashima et al 2011), and dust lofting (Hartzell et al 2013;Wang et al 2016). These tests are difficult and costly to run however, as they often rely on parabolic flights, drop-tower set-ups, or shuttle missions to reach variable gravity conditions.…”

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confidence: 99%

Validating N-body code chrono for granular DEM simulations in reduced-gravity environments

Sunday

Murdoch

Tardivel

et al. 2020

Monthly Notices of the Royal Astronomical Society

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The Discrete Element Method (DEM) is frequently used to model complex granular systems and to augment the knowledge that we obtain through theory, experimentation, and real-world observations. Numerical simulations are a particularly powerful tool for studying the regolith-covered surfaces of asteroids, comets, and small moons, where reduced-gravity environments produce ill-defined flow behaviors. In this work, we present a method for validating soft-sphere DEM codes for both terrestrial and small-body granular environments. The open-source code Chrono is modified and evaluated first with a series of simple two-body-collision tests, and then, with a set of piling and tumbler tests. In the piling tests, we vary the coefficient of rolling friction to calibrate the simulations against experiments with 1 mm glass beads. Then, we use the friction coefficient to model the flow of 1 mm glass beads in a rotating drum, using a drum configuration from a previous experimental study. We measure the dynamic angle of repose, the flowing layer thickness, and the flowing layer velocity for tests with different particle sizes, contact force models, coefficients of rolling friction, cohesion levels, drum rotation speeds and gravity levels. The tests show that the same flow patterns can be observed at Earth and reduced-gravity levels if the drum rotation speed and the gravity-level are set according to the dimensionless parameter known as the Froude number. Chrono is successfully validated against known flow behaviors at different gravity and cohesion levels, and will be used to study small-body regolith dynamics in future works.

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“…Others conducted experiments with much faster projectiles, closer to the speed used for the Hayabusa2 sampling mechanism: for example Yamamoto et al (2005) looked at the velocity distribution of ejecta, Yamamoto et al (2009) at the transient crater growth, and Nakamura et al (2013) at the penetration depth of the impactor. Experiments have even been possible under low-gravity or microgravity, through the use of an Atwood machine (Murdoch et al 2017) or parabolic flights (Nakamura et al 2013;Brisset et al 2018).…”

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confidence: 99%

Numerical modelling of medium-speed impacts on a granular surface in a low-gravity environment application to Hayabusa2 sampling mechanism

Thuillet

Michel

Tachibana

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Even if craters are very common on Solar System body surfaces, crater formation in granular media such as the ones covering most of visited asteroids still needs to be better understood, above all in low-gravity environments. JAXA’s sample return mission Hayabusa2, currently visiting asteroid (162173) Ryugu, is a perfect opportunity for studying medium-speed impacts into granular matter, since its sampling mechanism partly consists of a 300 m s−1 impact. In this paper, we look at medium-speed impacts, from 50 to 300 m s−1, into a granular material bed, to better understand crater formation and ejecta characteristics. We then consider the sampler horn of Hayabusa2 sampling mechanism and monitor the distribution of particles inside the horn. We find that the cratering process is much longer under low gravity, and that the crater formation mechanism does not seem to depend on the impact speed, in the considered range. The Z-model seems to rightly represent our velocity field for a steady excavation state. From the impact, less than $10{{\ \rm per\ cent}}$ is transmitted into the target, and grains are ejected mostly with angles between 48° and 54°. Concerning the sampling mechanism, we find that for most of the simulations, the science goal of 100 mg is fulfilled, and that a second impact increases the number of ejecta but not necessarily the number of collected particles.

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An experimental study of low-velocity impacts into granular material in reduced gravity

Cited by 24 publications

References 43 publications

Numerical modeling of lander interaction with a low-gravity asteroid regolith surface

Numerical modeling of lander interaction with a low-gravity asteroid regolith surface

Validating N-body code chrono for granular DEM simulations in reduced-gravity environments

Numerical modelling of medium-speed impacts on a granular surface in a low-gravity environment application to Hayabusa2 sampling mechanism

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