Abstract As small celestial body exploration advances, higher requirements with regard to system safety and landing precision are proposed for future landing and sample return missions. However, due to limited prior information about the target, the complex dynamics environment, and significant time-delay, performing a descent and landing on the small body surface is challenging. Among all the techniques required for achieving a safe landing, onboard guidance, navigation, and control (GNC) is of paramount importance in determining mission success. In this paper, a systematic survey of the autonomous GNC technologies for descent and landing on small bodies is carried out. First, based on an analysis of the technical challenges in the process, an overview of typical small body landing and sample return missions is given. Then, an elaboration of the state-of-the-art GNC technologies is presented. Specifically, autonomous navigation methods in unknown environments with highly-nonlinear dynamics are introduced. Descent guidance and control algorithms that take into account landing performance optimization and system robustness against model uncertainties are discussed. Touchdown dynamics and control methods proposed for precise and safe surface contact under weak gravity are analyzed. And safe strategies for onboard detected emergencies such as collision threats and system malfunctions are explained. Besides the prevalent methods, innovative techniques with respect to observability-based optimization, edge curve matching, online landing site selection, collision probability-based hazard avoidance, and trajectory curvature guidance proposed for improving system safety and landing performance are elucidated. At last, based on the growing system autonomy and operational complexity demands, a prospect of future research directions for small body GNC technologies is given.

中文翻译：

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小天体下降着陆自主GNC技术的最新进展

摘要 随着小天体探测的推进，对未来的着陆和样本返回任务对系统安全性和着陆精度提出了更高的要求。然而，由于关于目标的先验信息有限、复杂的动力学环境和显着的时延，在小体表上执行下降和着陆具有挑战性。在实现安全着陆所需的所有技术中，机载制导、导航和控制 (GNC) 是决定任务成功的最重要因素。在本文中，对用于小体下降和着陆的自主 GNC 技术进行了系统调查。首先，基于对过程中技术挑战的分析，概述了典型的小体着陆和样本返回任务。然后，详细介绍了最先进的 GNC 技术。具体而言，介绍了具有高度非线性动力学的未知环境中的自主导航方法。讨论了考虑着陆性能优化和系统对模型不确定性的鲁棒性的下降引导和控制算法。分析了在弱重力下为精确和安全的表面接触提出的着陆动力学和控制方法。并解释了车载检测到的紧急情况（例如碰撞威胁和系统故障）的安全策略。除了流行的方法，基于可观察性的优化、边缘曲线匹配、在线着陆点选择、基于碰撞概率的危险规避等创新技术，并阐明了为提高系统安全性和着陆性能而提出的轨迹曲率制导。最后，基于日益增长的系统自主性和操作复杂性需求，展望了小体GNC技术的未来研究方向。