## 1 Introduction
The pathfinder satellite and the geosynchronous space situational awareness program are part of the U.S. Air Force space-based surveillance system program [12]. In Europe, ESA supported and is still supporting several research programs for space-based SSA, such as the space-based space surveillance service [13], the optical In-situ Monitor project [14], A summary of ESA activities related to space-based optical observations of space debris and NEOs is reported in [15]. All of the above missions are designed with dedicated payloads, but most satellites already have one or more-star trackers for attitude determination, which, if properly utilized, can constitute a zero-cost space surveillance system. Using the star as the reference frame for attitude measurement, the star trackers can output the vector direction of the star in the coordinates of the star trackers, thus providing highly accurate measurement data for spacecraft attitude control and astronomical navigation. The star map taken by the star trackers contains not only stars but also space targets, such as space debris [16]. In the starry background, space debris can also reflect part of the energy from the Sun and has similar luminous characteristics to the stars. When the signal-to-noise ratio is high enough, space debris can be captured by star trackers, and all its information is contained in the point target of the star map. Combined with the principle of extracting star points and star map recognition of star trackers [17], it can distinguish space targets from stars. In simple terms, the identification of all the stars in the star map is accomplished with the help of star trackers, and the targets are naturally filtered out. In fact, in multi-star tracker missions, one or more sensors are usually not used to determine the attitude. Therefore, the images acquired in these sensors can be used for surveillance operations. In this way,unlike most space-based missions designed specifically for space situational awareness, no specific attitude maneuver is required [18]. The proposed strategy has also been discussed in previous literature. In [19], a convolutional filter-based centroid estimation image preprocessing was first used. Then, stars were removed using the pyramidal star identification technique, and finally, the spatial target was tracked by combining the center-of-mass estimation and the Kalman filter. However, this work did not address the orbiting of space targets. The initial possibility of using a star tracker for space target detection was discussed in [20]. The idea is to use convolutional neural networks, which is interesting but not feasible with the current technology of spacecraft applications. In [21], a faint streak detection algorithm based on a streak-like spatial filter was proposed, but it took 2-3 h for 4000 \(\times\) 4000-pixel images. Considering the limited computing power of spacecraft on-board computers, none of these techniques is designed for efficient implementation. Therefore, research on novel observation methods to improve the cost-effectiveness of observation is the main research direction at present. In this paper, the configuration of a space debris monitoring network based on multiple star trackers is proposed and studied for detection feasibility. Unlike the previous algorithms, the proposed algorithm uses satellite equipped star trackers to detect and extract space targets from star maps taken during star tracker attitude fixation and mines the available observation information of space targets from a large amount of data to achieve space target surveillance, thus saving the cost of launching dedicated surveillance satellites. The space target is observed by a single satellite star tracker and the target orientation data are given.