## 2 The Evolution of Space Situational Awareness Policies
The report systematically summarized the development of the European space monitoring and space target tracking system during that period, providing prospects for the future development of the system in both technical and managerial aspects, underscoring European high regard for constructing a space target monitoring system [22]. In 2022, European leaders proposed considering space as a strategic zone for Europe and called for the formulation of a European Space Security and Defense Strategy. In response, the European Commission put forth the first European Space Security and Defense Strategy, emphasizing the prominent position of space situational awareness [23; 24]. Presently, aligning with the European development plan for its space situational awareness system, Europe has established ground radar systems, such as the Grand Reseau Adapte a la Veille Spatiale (GRAVES), for space situational awareness. Concurrently, the EU is planning to respectively launch the Hera satellite in 2024 and the ClearSpace-1 satellite in 2026 to carry out tasks related to space debris cleanup. Plans are also underway to launch the Vigil satellite in the 2020s to monitor the space environment, gradually advancing toward the goal of constructing the European space situational awareness and space defense system. Figure 4 shows the important milestones in the development of European space situational awareness policies. In addition to the United States and Europe, Russia has developed its space situational awareness system known as the Russian Space Surveillance System (RSSS) [25]. The origins of the Russian space situational awareness system can be traced back to the Soviet era in the 1960s when a world-class network of ground-based radar stations and optical telescopes was established, ensuring the efficient monitoring of space targets [26]. Moreover, owing to historical factors, Russia has maintained a top-tier level of theoretical research in the field of space situational awareness [27]. In recent years, India has demonstrated a growing interest in space situational awareness. India established the Directorate of Space Situational Awareness and Management and, in 2019, initiated the construction of the Space Situational Awareness Control Centre to specifically oversee India's activities and research programs in space situational awareness [28; 29]. In 2022, India entered into a cooperation agreement with the United States, covering aspects such as the sharing of space situational awareness information [30]. Additionally, starting from 2022, the Indian Space Research Organisation (ISRO) has annually released a Space Situational Assessment Report on its official website. This report provides information on the global launch scenario and typical space collision risks of the previous year, highlights future trends in space situation, and offers insights into the development in the field of space situational awareness [31; 32]. Japan is also in the planning stages for constructing a space-based situational awareness system composed of radars, optical telescopes, and analysis systems. The goal is to monitor space debris and analyze its potential threats to on-orbit satellites and astronauts [33]. In general, the concept of space situational awareness emerged in the 1990s and has garnered widespread attention in the 21 st century. With the ongoing advancement of space technology, the concept of space situational awareness has evolved, expanding from its initial focus on the discovery and perception of space objects to encompass the measurement and estimation of the motion states of these objects, continuous monitoring of key space targets and regions, orbit prediction of space objects, and warning of collision threats. Figure 4: The development of Europe SSA policies. Looking ahead, as space technology continues to advance, more complex space missions will demand higher requirements for the scope and precision of space situational awareness.