# A Safety Prediction System for Lunar Orbit Rendezvous and Docking Mission
## 1 Introduction  
As the only natural satellite of the Earth, the importance of the Moon to the Earth and mankind is self-evident. The Cislunar environment is a promising location for space exploration. Apollo carried out eight crewed manual lunar orbital rendezvous and docking missions, in which human intelligence played an important role in rendezvous monitoring and docking [1]. Space rendezvous and docking technology refers to the technology in which the chaser spacecraft and the target spacecraft meet at a certain position on the same orbit at a certain time, and then are structurally connected. Compared with traditional rendezvous and docking relying on ground control, autonomous rendezvous and docking can reduce the work intensity of ground personnel, eliminate the influence of signal delay and avoid external interference. Autonomous rendezvous and docking mean that the two spacecraft rely on their own navigation, guidance and control systems to complete the entire process of rendezvous and docking without the intervention of personnel on the ground or in the spacecraft [2, 3]. An autonomous rendezvous requires the formulation of high-precision, high-reliability and high-safety rendezvous strategies, and higher requirements for the performance and intelligence of the guidance, navigation and control system [4, 5, 6]. The composition of an autonomous rendezvous and docking system is shown in Figure 1.  
The guidance, navigation and control for close operations of spacecraft has always been a hot research topic in the field of space technology. For example, [PERSON] et al. [7] and [PERSON] et al. [8] focused their attention on approaches to rendezvous in lunar Near Rectilinear Halo Orbits (NRHO). [PERSON] et al. [9] designed a GNC system for 6 degrees of freedom (6 DOF) coupled Cislunar rendezvous and docking. Research on the Orion vehiclehas also been conducted [10; 11]. There are many rendezvous and docking strategies. In the close-range phase, the glideslope trajectory is known as a simple approaching trajectory complying to safety constrains, and the common approach directions are known as V-bar and R-bar [12; 13]. Techniques such as sliding mode control [14], artificial potential function [15], genetic algorithms [16], searching strategy [17] and model predictive control [18] are all involved in the research field of rendezvous and docking. In this paper, we design an auxiliary system to predict the safety level of the rendezvous and docking process.  
In the control process of the ground flight for autonomous rendezvous and docking missions in the third phase of lunar exploration, by drawing lessons the idea of solving the problem of scale ambiguity in the relative pose estimation of non-cooperative targets with the combination of monocular camera and LIDAR [19], we perform feature matching, extraction and target classification on the target image captured by the surveillance camera on the chaser. We design an auxiliary prediction system for engineering applications, which can improve the intelligent level of flight control, effectively assist ground personnel in data monitoring and mission decision-making and increase the mission success rate.  
The remainder of this paper is organized as follows. In Section 2, we clarify the mission objectives, and analyze the needs and difficulties. In Section 3, we propose a framework for the autonomous judgment of human-machine collaboration safety and give the system's function division and design scheme. Section 4 describes the experimental verification of the system. Section 5 is the conclusion.