Motion reconstruction of the small carry-on impactor aboard Hayabusa2

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https://doi.org/10.1007/s42064-020-0077-6

Motion reconstruction of the small carry-on impactor aboard Hayabusa2 Takanao Saiki1 (), Yuya Mimasu1 , Yuto Takei1 , Manabu Yamada2 , Hirotaka Sawada1 , Kazunori Ogawa1,3 , Naoko Ogawa1 , Hiroshi Takeuchi1,4 , Akira Miura1,4 , Yuri Shimaki1 , Koji Wada2 , Rie Honda5 , Yasuhiro Yokota1,5 , Kei Shirai3 , Naruhisa Sano6 , Hirohito Ohtsuka6 , Go Ono1 , Kent Yoshikawa1 , Shota Kikuchi1 , Chikako Hirose1 , Yukio Yamamoto1,4 , Takahiro Iwata1,4 , Masahiko Arakawa3 , Seiji Sugita2,7 , Satoshi Tanaka1,4 , Fuyuto Terui1 , Makoto Yoshikawa1,4 , Satoru Nakazawa1 , Sei-ichiro Watanabe1,8 , and Yuichi Tsuda1,4 1. 2. 3. 4. 5. 6. 7. 8.

Japan Aerospace Exploration Agency, Sagamihara 252-5210, Japan Chiba Institute of Technology, Narashino 275-0016, Japan Kobe University, Kobe 657-8501, Japan The Graduate University for Advanced Studies, Sagamihara 252-5210, Japan Kochi University, Kochi 780-8520, Japan IHI Aerospace Co., Ltd., Tomioka 370-2398, Japan The University of Tokyo, Tokyo 113-0033, Japan Nagoya University, Nagoya 464-8601, Japan

ABSTRACT

KEYWORDS

Subsurface exploration is one of the most ambitious scientific objectives of the Hayabusa2

small body exploration

mission. A small device called small carry-on impactor (SCI) was developed to create an

Hayabusa2

artificial crater on the surface of asteroid Ryugu. This enables us to sample subsurface

kinetic impact

materials, which will provide a window to the past.

artificial crater

The physical properties of the

resulting crater are also useful for understanding the internal structure of Ryugu. Accurate

motion reconstruction

understanding of the crater and ejecta properties, including the depth of excavation of subsurface materials, requires accurate information on impact conditions. In particular, the impact angle is a critical factor because it greatly influences the size and shape of the crater. On April 5, 2019, the Hayabusa2 spacecraft deployed the SCI at 500 m of altitude above the asteroid surface. The SCI gradually reduced its altitude, and it shot a 2 kg copper projectile

Research Article

into the asteroid 40 min after separation. Estimating the position of the released SCI is

Received: 27 Januany 2020

essential for determining the impact angle. This study describes the motion reconstruction of

Accepted: 26 March 2020

the SCI based on the actual operation data. The results indicate that the SCI was released

© Tsinghua University Press

with high accuracy.

1

Introduction

Hayabusa2 was developed by Japan Aerospace Exploration Agency (JAXA) as an asteroid sample-return spacecraft [1, 2]. It was launched on December 3, 2014, by the Japanese H2A launch vehicle. It is a round trip mission similar to that of Hayabusa. Hayabusa explored asteroid Itokawa—a small S-type asteroid, and it returned to Earth with sample materials in 2010 [3–8]. The target body of Hayabusa2 is asteroid 162173 Ryugu. Ryugu



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2020

is a near-Earth C-type asteroid, which is expected to contain organic and hydrated m