Objective Geosynchronous orbit (GEO) satellites are a critical component of global telecommunications and navigation systems, but they are also vulnerable to potential collisions or hostile interactions with other space objects. Therefore, the ability to accurately perceive the approach behavior of these objects is paramount for enhancing the safety and autonomy of GEO spacecraft. This paper proposes a sophisticated and reliable method for detecting the approach behavior of GEO space objects only using line-of-sight measurements of objects derived from optical imaging sensors. Existing methods often rely on distance measurements, which can be challenging to obtain accurately in space environments. Research in this paper aims to overcome this limitation by utilizing only line-of-sight information of objects, which is readily available from optical sensors. By analyzing the temporal variations in azimuth and elevation angles, we aim to identify patterns that are indicative of an approaching object and develop algorithms to accurately perceive the approach behavior of these objects.

Methods To achieve this objective, a comprehensive analytical framework is presented. First, the effects of illumination conditions and the sensitivity of the optical sensor on the object's visibility are considered (Fig.2). Second, the azimuth and elevation angle variations of a GEO object relative to a mission spacecraft are analyzed to identify patterns that are indicative of an approaching object (Fig.4). As the object approaches, the magnitude of variations in the tangent of the azimuth angle increases over time (Fig.5), providing a potential signature for perception. By leveraging the orbital periodicity of the space object and the consistency of its visible arcs, the proposed method correlates multiple observation segments (Fig.7), fits the temporal trend of the azimuth angle tangent, predicts extreme values, and monitors the pattern of these extremes to accurately perceive the object's approach behavior.

Results and Discussions Simulations were conducted to evaluate the performance of the proposed method (Fig.8). The results demonstrate that the method is capable of accurately detecting the approach of GEO objects using only line-of-sight measurements from optical imaging sensors. Specifically, the method achieved an accuracy rate of over 96% in identifying approaching objects using only three orbital periods of data, with each orbital period containing effective segments greater than 30 minutes (Tab.2). This high accuracy indicates that the method can provide valuable information for spacecraft self-defense systems, enabling them to detect potential threats at an early stage. Furthermore, the method exhibits several advantages over traditional methods that rely on distance measurements. First, it does not require additional sensors or instrumentation for distance measurements, thus reducing the complexity and cost of the overall system (Fig.10). Second, it is robust to variations in illumination conditions and sensor sensitivity, ensuring reliable performance in a range of environmental conditions. Finally, the method's simplicity and efficiency make it suitable for real-time implementation on spacecraft with limited computational resources.

Conclusions A method for detecting the approach behavior of GEO space objects only using line-of-sight measurements of objects derived from optical imaging sensors is designed, by leveraging the unique patterns in the temporal variations of azimuth and elevation angles. This method represents a significant advancement in the field of space safety and security, as it overcomes the limitations of traditional distance-based methods and provides a reliable means for autonomous threat detection. The simplicity and efficiency of the proposed method make it suitable for real-time implementation on spacecraft, enabling them to detect potential threats at an early stage. In summary, this research has laid the foundation for a new paradigm in space object perception and trackin, leveraging line-of-sight information from optical sensors to provide enhanced capabilities for spacecraft self-defense and situational awareness.