Design and flight results of GNC systems in Hayabusa2 descent operations

Hayabusa2 is a Japanese sample return mission from the near-Earth asteroid Ryugu. The Hayabusa2 spacecraft was launched on December 3, 2014, and reached the asteroid on June 27, 2018. It remained there until November 13, 2019 for in situ observation and soil sample collection and will return to the Earth in November or December 2020. During its stay at the asteroid, Hayabusa2 performed descent operations 16 times. This paper presents an overview of a guidance, navigation, and control method used in such descent operations. The method consists of on-board and on-ground guidance systems to control the spacecraft and an image-based navigation technique that uses a shape model and ground control points of the asteroid. Flight results in the first touchdown operation are shown as an example, which demonstrate that the method showed a good performance overall and contributed to the success of the mission.