# Research on Space-Based Visible Detection for Conical Space Targets
## 1 Introduction  
With the acceleration of human space exploration, the number of spacecraft in orbit, mainly represented by artificial satellites, has increased rapidly. Because spacecraft recovery technology is expensive and difficult to deploy, when an on-orbit spacecraft fails and is scrapped, it will rarely be recovered, and will instead be left to drift around in orbit. Collision with these failed spacecraft will cause the running spacecraft to malfunction or even disintegrate, posing a serious threat to the safe operation of orbiting spacecraft [1; 2]. The first satellite collision event in human history occurred over Siberia on 11 February 2009, when an Iridium satellite launched by the United States in 1997 collided with a Cosmos2251 satellite launched by Russia in 1993, highlighting the importance of deploying space target monitoring systems [3; 4]. As the space environment grows increasingly complicated, countries represented by the United States are putting in place a strategic layout of space-based space target surveillance systems to improve their ability to govern space resources [5]. The Midcourse Space Experiment (MSX) satellite was launched by the United States in 1996. The MSX satellite is equipped with a 150 mm caliber space-based visible (SBV) sensor, which is used to follow communication satellites in geostationary orbit as well as certain other high-orbit spacecraft [6]. The Block 10 Pathfinder satellite, the first satellite of the space-based space surveillance (SBSS) system, was successfully launched and operated by the United States in 2010, marking the official entry of space target surveillance into the space-based era [7]. The SBSS system is expected to boost U.S. space target monitoring capabilities by 50%, covering a wide range of orbital and ballistic targets in medium, high, and low orbits, and detecting target characteristics. In addition, in 2014, the U.S. and Canada jointly launched the \"Sapphire\" satellite, which has a photoelectric sensor for tracking and monitoring high-orbit space targets, as well as providing space situational awareness capabilities [8; 9]. The monitoring of space-based space targets will become common in the future, thanks to the faster deployment of the high-throughput big satellite constellation. The high-speed interconnected satellite constellations may perform regionally coordinated observations as well as worldwide ubiquitous perception, constituting a \"skynet\" for future space target surveillance. The system caliber is one of the most critical elements that influences the resolution of a space target monitoring system and, therefore, indirectly determines target detection accuracy. Visible detection is a popular method of space detection because of its high detection accuracy, intuitive nature, and low elevation angles that are less impacted by ground clutter [10; 11]. Visible detection provides distinct benefits for space objects that do not create heat on their own. As a result, the caliber determination technique of the space-based visible space target detection system is investigated in this study [12; 13; 14]. Because the space-based visible space target detection system detects the target by receiving the radiation energy reflected by the space target, the reflected radiation models established by space targets of various shapes differ, in other words, the shape of the target will affect the reflected radiation energy and, in turn, the radiation intensity received by the detector. Because satellites are the most observable space targets, this article focuses on satellites as the detection object. The satellite's main body has a variety of forms, such as spherical, conical, cylindrical, polyhedron-based, prism-like, and dumbbell-like shapes [15; 16; 17]. The most popular artificial satellites are spheres and cones, and the spherical target's reflected radiation model is a subset of the conical target model [13].