Dr. Patrick Michel Directeur de Recherches au CNRS Rudy Valette, Elie Hachem, Stephen Schwartz, Florian Thuillet (PhD) Granular material dynamics and space missions to celestial bodies: a transdisciplinary approach Academy 3 & Academy 2
The main asteroid belt (7561) PatrickMichel
ASTEROiDS: Great diversity in sizes, shapes, composition 320 m 950 km Image: NASA/JPL-Caltech/JAXA/ESA
Granular material is present on all visited asteroid surfaces Asteroid Itokawa (320 m) • Visited by Hayabusa in 2005 • Sample returned to Earth on June 13, 2010 Image: JAXA Image: Miyamoto et al, 2007
OSIRIS-REx & Hayabusa2 2018-2020 Images of 2 new worlds (need good interpretations) Lander deployment Bennu Two kinds of sampling methods 535 m
Project goal Compare two approaches used to model granular material dynamics: – The continuum approach (Ecole des Mines ParisTech) – The soft-sphere discrete element method (OCA) Apply the two approaches (separated or combined) to model: – Lander bouncing on asteroid surfaces (Hayabusa2) – Sampling of asteroid surfaces – Asteroid regolith surface processes
First Comparison continuum versus discrete approach: Split Shear Cell Experiment Courtesy: Martin van Hecke
Split Shear Cell Experiment Soft-Sphere Discrete Element Method Modeling of grains as discrete elements solving for all contact forces (sliding rolling, twisting …)
Split Shear Cell Experiment Soft-Sphere Discrete Element Method Width of ß Experiment à the shear Colored band grains (b) (a) Further Initial in time state ß Simulation à
Split Shear Cell Experiment Continuum Approach Actual models fail for low shear rates and close to walls, free surfaces, or discontinuities The wide shear bands may be predicted by adding nonlocality in continuum models Henann & Kamrin (2013), PNAS 425 , 256. Fenistein et al. (2004), wide shear band PRL 92-9 , 094301. The shear band is way too wide and gets wider and wider (no finite shear band)
Current investigations Landslide experiments Goal: reproduce the avalanche angle with both the continuum and the soft-sphere approaches
Perspectives Applications of Continuum versus Soft- Sphere to space mission devices and asteroid surface processes Decision tool for: sampling site selections, lander detection, inference of regolith properties
Interactions within UCA and outside Within UCA: – Ecole des Mines ParisTech, GéoAzur Outside UCA: – NASA, JAXA, ESA, DLR – Univ. Maryland – Technische Universität Braunschweig – Arizona State University – MIT – Tsuangh University – John Hopkins University – Chyba Institute of Technology
Students Florian Thuillet (SupAéro Engineer, Bourse UNS), Lagrange Lab. Clara Maurel (SupAéro Engineer) MIT, co- tutelle in project with UNS Yun Zhang, Tsuangh University, China Note: F. Thuillet & Y. Zhang are award winners for the • best presentations at the Planetary Defense Conference (Tokyo, May 2017)
Publications Communications in international conferences: – Schwartz, S.R., Maurel, C., Ballouz, R.L., Richardson, D.C., Michel, P., Valette, R., Hachem, E. 2017. Vibration-driven segregation of regolith on low-gravity asteroids . Asteroids comets Meteors 2017, oral presentation, Montevideo (Uruguay) – Thuillet, F., Maurel, C., Michel, P., Biele, J., Ballouz, R.-L., Richardson, D.C. 2017. Numerical modeling of interactions of a lander with low-gravity asteroid regolith surfaces . Planetary Defense Conference 2017, best presentation, Tokyo (Japan) – Thuillet, F., Maurel, C., Michel, P., Biele, J., Ballouz, R.-L., Richardson, D.C. 2017. Simulations of regolith response to a low-speed impact of a lander in a low-gravity environment: application to the lander MASCOT on Hayabusa2 . Oral presentation at the Japan Geophysical Union-American Geophysical Union meeting, Chyba (Japan) – Thuillet, F., Maurel, C., Michel, P., Biele, J., Ballouz, R.-L., Richardson D.C. 2017. Numerical simulations of surface package landing on a low-gravity granular surface: Application to the landing of mascot onboard Hayabusa2. Lunar and Planetary Science Congress (LPSC) 2017, The Woodlands (Texas).
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