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Modified granular impact force laws for the OSIRIS-REx touchdown on the surface of asteroid (101955) Bennu
  • +13
  • Ronald-Louis Ballouz,
  • Kevin Walsh,
  • Paul Sanchez,
  • Keith Holsapple,
  • Patrick Michel,
  • Dan Scheeres,
  • Yun Zhang,
  • Derek Richardson,
  • Olivier Barnouin,
  • Mike Nolan,
  • Edward Bierhaus,
  • Stephen Schwartz,
  • Onur Celik,
  • Mitsuhisa Baba,
  • Harold Connolly, Jr.,
  • Dante Lauretta
Ronald-Louis Ballouz
University of Arizona

Corresponding Author:[email protected]

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Kevin Walsh
Southwest Research Institute, Boulder, CO
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Paul Sanchez
University of Colorado Boulder, CO, USA
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Keith Holsapple
P.O.Box 305, Medina, WA 98039, USA
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Patrick Michel
Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France
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Dan Scheeres
University of Colorado Boulder, CO, USA
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Yun Zhang
Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France
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Derek Richardson
University of Maryland, College Park, MD, USA
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Olivier Barnouin
The Johns Hopkins University Applied Physics Laboratory, Laurel, MD, USA
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Mike Nolan
Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
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Edward Bierhaus
Lockheed Martin Space, Littleton, CO, USA
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Stephen Schwartz
Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
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Onur Celik
University of Glasgow, Scotland, UK
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Mitsuhisa Baba
Institute of Space and Astronautical Studies, JAXA, Sagamihara, Japan
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Harold Connolly, Jr.
Dept. of Geology, Rowan University, Glassboro, NJ, USA
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Dante Lauretta
Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
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Abstract

The OSIRIS-REx mission collected a sample from the surface of the asteroid (101955) Bennu in October 2020. Here we study the impact of the OSIRIS-REx Touch-and-Go Sampling Acquisition Mechanism (TAGSAM) interacting with the surface of an asteroid in the framework of granular physics. Traditional approaches to estimating the penetration depth of a projectile into a granular medium include force laws and scaling relationships formulated from laboratory experiments in terrestrial-gravity conditions. However, it is unclear that these formulations extend to the OSIRIS-REx scenario of a 1300-kg spacecraft interacting with regolith in a microgravity environment. We studied the TAGSAM interaction with Bennu through numerical simulations using two collisional codes, pkdgrav and GDC-i. We validated their accuracy by reproducing the results of laboratory impact experiments in terrestrial gravity. We then performed TAGSAM penetration simulations varying the following geotechnical properties of the regolith: packing fraction (P), bulk density, inter-particle cohesion (σc), and angle of friction (ɸ). We find that the outcome of a spacecraft-regolith impact has a non-linear dependence on packing fraction. Closely packed regolith (P≳0.6) can effectively resist the penetration of TAGSAM if ɸ≳28° and/or σc≳50 Pa. For loosely packed regolith (P≲0.5), the penetration depth is governed by a drag force that scales with impact velocity to the 4/3 power, consistent with energy conservation. We discuss the importance of low-speed impact studies for predicting and interpreting spacecraft-surface interactions. We show that these low-energy events also provide a framework for interpreting the burial depths of large boulders in asteroidal regolith.