One of the major challenges in the Hayabusa2 sample-return mission was the second touchdown on the asteroid Ryugu, which was designed to collect subsurface materials near the artificial crater formed by a small carry-on impactor. Due to engineering and scientific requirements, a narrow area with a radius as small as 3.5 m was selected as the target landing site. To achieve pinpoint touchdown at the selected site, an artificial landmark called a target marker (TM) was used for optical navigation. The key to a successful touchdown was precise deployment of the TM in the microgravity environment of the asteroid. This study therefore investigates a viable trajectory for TM deployment, incorporating the uncertainty in the impact and rebound motions of the TM. Following the TM deployment operation, a detailed survey of the landing site around the TM settlement point is performed to assess the terrain conditions. To guarantee the observation quality and spacecraft safety, multi-impulse low-altitude trajectories are introduced in this paper, along with covariance analyses based on the high-fidelity polyhedral gravity model of Ryugu. Subsequently, a pinpoint touchdown trajectory that satisfies various engineering requirements, such as landing accuracy and velocity, is designed, taking advantage of optical TM tracking. The feasibility of the touchdown sequence is further validated by a Monte Carlo dispersion analysis. Consequently, Hayabusa2 successfully touched down within the target site on 11 July 2019. The current research also conducts a post-operation trajectory reconstruction based on the flight data to demonstrate the actual guidance performance in the TM deployment, landing site observations, and pinpoint touchdown.

Hayabusa2 样本返回任务的主要挑战之一是小行星 Ryugu 的第二次着陆，该任务旨在收集由小型随身撞击器形成的人造陨石坑附近的地下物质。由于工程和科学需要，选择了半径小至3.5 m的狭窄区域作为目标着陆点。为了在选定地点实现精确着陆，使用称为目标标记 (TM) 的人工地标进行光学导航。成功着陆的关键是在小行星的微重力环境中精确部署 TM。因此，这项研究调查了 TM 部署的可行轨迹，并结合了 TM 冲击和回弹运动的不确定性。在 TM 部署操作之后，对 TM 定居点周围的着陆点进行了详细调查，以评估地形条件。为保证观测质量和航天器安全，本文引入了多脉冲低空轨迹，并基于龙宫高保真多面体重力模型进行协方差分析。随后，利用光学 TM 跟踪设计了满足各种工程要求（如着陆精度和速度）的精确着陆轨迹。达阵序列的可行性通过蒙特卡罗分散分析得到进一步验证。因此，隼鸟 2 号于 2019 年 7 月 11 日成功降落在目标地点。