Modified granular impact force laws for the OSIRIS-REx touchdown on the surface of asteroid (101955) Bennu

作者：Ronald‐Louis Ballouz, K. J. Walsh, Paul Sánchez, K. A. Holsapple, Patrick Michel, Daniel J. Scheeres, Y. Zhang, D. C. Richardson, O. S. Barnouin, M. C. Nolan, E. B. Bierhaus, H. C. Connolly, S. R. Schwartz, Onur Çelik, Masahiro Baba, D. S. Lauretta · 发表于：Monthly Notices of the Royal Astronomical Society · 年份：2021 · DOI：10.1093/mnras/stab2365 · 被引用次数：47 · 研究领域：Astro and Planetary Science、Planetary Science and Exploration、High-pressure geophysics and materials

ABSTRACT The OSIRIS-REx mission collected a sample from the surface of the asteroid (101955) Bennu in 2020 October. 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 (ϕ). 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 ϕ ≳ 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 cons...