[P-PS02] Regolith Science

[PPS02-03] Loose packing of Bennu's near-subsurface

*Kevin J Walsh¹, Ronald-Louis Ballouz^2,3, Erica R Jawin⁴, Chrysa Avdellidou⁵, Olivier S Barnouin³, Carina A Bennett², Edward B Bierhaus⁶, Brent J Bos⁷, Saverio Cambioni⁸, Harold C Connolly Jr.⁹, Marco Delbo⁵, Daniella N DellaGiustina², Joseph DeMartini¹⁰, Joshua P Emery¹¹, Dathon R Golish², Patrick C Haas⁶, Carl W Hergenrother², Huikang Ma⁶, Patrick Michel⁵, Michael C Nolan², Ryan Olds⁶, Benjamin Rozitis¹², Derek C Richardson¹⁰, Bashar Rizk², Andrew J Ryan², Paul Sanchez¹³, Daniel J Scheeres^13,14, Stephen R Schwartz², Sanford H Selznick¹⁵, Yun Zhang⁵, Dante S Lauretta² (1.Southwest Research Institute, Boulder, 2.Lunar and Planetary Laboratory, University of Arizona, 3.Johns Hopkins University Applied Physics Laboratory, 4.National Air and Space Museum, Smithsonian Institution, 5.Université Côte d’Azur, Observatoire de la Côte d’Azur, 6.Lockheed Martin Space, 7.NASA Goddard Spaceflight Center, 8.Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 9.Department of Geology, Rowan University, 10.Department of Astronomy, University of Maryland, 11.Department of Astronomy and Planetary Science, Northern Arizona University, 12.School of Physical Sciences, The Open University, 13.Colorado Center for Astrodynamics Research, University of Colorado Boulder, 14.Smead Aerospace Engineering Sciences Department, University of Colorado Boulder, 15.Ascending Node Technologies)

Keywords:Asteroid, Regolith, Bennu

The OSIRIS-REx spacecraft interaction with Bennu provided a valuable
test of its near-subsurface properties. The spacecraft was equipped
with a Touch-and-Go Sample Acquisition Mechanism (TAGSAM), which is an
annular container attached to an extendable arm. On 20 October 2020
the sampling operation successfully pressed TAGSAM into the surface of
the asteroid at 10 cm/s, released high pressure gas and after a few
seconds of contact initiated a backaway manuever to leave Bennu.

The interaction with the surface prior to gas release was bracketed
with two images of the surface with ~mm/pixel resolution and the
forces imparted on the spacecraft were recorded with a Inertial
Measurement Unit. We combine this data to estimate the penetration
profile of TAGSAM into the near-subsurface of Bennu, characterizing
peak accelerations during the extent of the interaction prior to gas
release. We utilize granular mechanics penetration force laws and
numerical modeling to constrain the packing fraction of material in
the upper few 10's cm of Bennu.