## 3 Typical Space-Based Situational Awareness Facilities
According to relevant research, this satellite carries a coaxial reflection system payload with an 85 mm aperture, a field-of-view angle of 2.08\({}^{\circ}\)\(\times\) 1.67\({}^{\circ}\), and a pixel size of 6.7 \(\upmu\)m, comprising 1280 \(\times\) 1024 pixels [39; 40]. To validate whether satellite maneuvers can enhance target detection capability, Canada launched the smallest space-based telescope to date, the Microvariability and Oscillations of Stars (MOST) satellite [41]. This satellite carries a 15 cm aperture optical telescope with a field-of-view angle of \(2^{\circ}\times 2^{\circ}\) and features 1024 \(\times\) 1024 pixels [42]. After the launch of the MOST satellite in Canada, the United States launched the Wide Area Space Surveillance System (WASS), utilizing a network of multiple LEO satellites to monitor stationary orbit targets on Earth. Each satellite in this system carries multiple wide-angle cameras, with each camera having a field-of-view angle of up to \(60^{\circ}\times 4^{\circ}\) and an aperture of 28 mm. The cameras are equipped with a long sunshade to achieve a 4\({}^{\circ}\) sun avoidance angle [41]. The most well-known space situational awareness satellite of Canada is the Sapphire satellite. This satellite employs a three-mirror anastigmat design which is similar to the SBV, with a 15 cm aperture and a field of view of 1.4\({}^{\circ}\). The detector of this satellite utilizes a trajectory speed mode to achieve a higher signal-to-noise ratio. It is capable of monitoring and tracking objects with a magnitude as faint as 15 [40; 42]. The space-based optical telescope (SBO), developed in Europe for space debris monitoring, features a CMOS sensor with an optical aperture of 20 cm, pixel size of 18 \(\upmu\)m, and a field-of-view angle of 6\({}^{\circ}\). It possesses robust capabilities for monitoring space debris targets, enabling observation of 2 cm-sized objects in HEO [39]. In addition, the AsteroidFinder satellite developed by Germany carries an optical payload with a 25 cm aperture. It employs an off-axis three-reflection dispersive imaging catadioptric optical system with a field-of-view angle of \(2^{\circ}\times 2^{\circ}\), pixel size of 13 \(\upmu\)m, and a resolution of 2k \(\times\) 2k pixels. By incorporating a field stop in the optical system, the camera of this satellite achieves effective stray light suppression, enabling the detection of spacecraft and space debris in LEO. This satellite validates the capability of space-based optical detection systems for detecting centimeter-sized space targets, marking a significant milestone in the development of space situational awareness systems [39; 40]. In general, space-based situational awareness facilities are predominantly equipped with an optical detection payload to monitor and assess space objects and the space environment. Compared to radar detection, optical detection is envisioned as the primary means for future space-based target monitoring. Optical detection consumes less energy for long-range detection and can be combined with real-time image processing to enhance resolution. In terms of monitoring capabilities, space-based situational awareness systems predominantly rely on visible light cameras as their effective payloads. However, due to the \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Satellite** & **Optical Aperture** & **Pixel Size** & **Pixel Number** & **Field of View** \\ \hline MSX & 15 cm & Unknown & Unknown & 1.4\({}^{\circ}\)\(\times\) 5.6\({}^{\circ}\) \\ SBSS & 30 cm & Unknown & 2.4 million & 3\({}^{\circ}\)\(\times\) 3\({}^{\circ}\) \\ STARE & 8.5 cm & 6.7 \(\upmu\)m & 1280 \(\times\) 1024 & 2.08\({}^{\circ}\)\(\times\) 1.67\({}^{\circ}\) \\ MOST & 15 cm & Unknown & 1024 \(\times\) 1024 & 2\({}^{\circ}\)\(\times\) 2\({}^{\circ}\) \\ Sapphire & 15 cm & Unknown & Unknown & 1.4\({}^{\circ}\) \\ SBO & 20 cm & 18 \(\upmu\)m & Unknown & 6\({}^{\circ}\) \\ Asteroid & 25 cm & 13 \(\upmu\)m & 2k \(\times\) 2k & 2\({}^{\circ}\)\(\times\) 2\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table}