## 6 Precise Orbit Determination Methods
As shown in Table 4, [PERSON] proposed the first analytical prediction algorithm for precisely determining the orbital elements of LEO objects [80]. Building upon that, [PERSON] et al. simplified the gravity model as well as the drag model and introduced the Simplified General Perturbations method (SGP) [81]. [PERSON] et al. further refined the SGP, leading to the development of the first practical orbit precise determination method, the SGP4, used by the North American Aerospace Defense Command (NORAD) [82; 83]. [PERSON] extended SGP4 and introduced the Simplified Deep-space Perturbation 4 method (SDP4) to precisely determine the orbits of deep-space targets [81]. [PERSON] et al. conducted an accuracy test on SDP4 and SGP4 using typical orbits. The results showed that SGP4/SDP4 models exhibit high computational speeds and can achieve the required accuracy for orbit prediction when dealing with near-circular orbits in MEO and GEO. The maximum deviation from the determined orbit to the nominal orbit was less than 3 km. However, for near-circular orbits with altitudes less than 50 km or highly eccentric orbits with eccentricity greater than 0.6 and perigee altitude less than 50 km, the computational results showed large discrepancies, and more precise computational models are needed to assist in updating the precise orbit determination of the targets [84; 85]. The convergence speed and accuracy are core indicators for evaluating the performance of precise orbit determination methods and can be influenced by various factors such as the performance of the orbit prediction model, distribution of observation arcs, accuracy of the observation data, data density, and more [86]. A systematic study conducted by the U.S. National Research Council on the impact of different factors on orbit prediction models revealed that factors including the accuracy of atmospheric drag models, solar radiation pressure models, gravity field models, the performance of orbit correlation and orbit propagation methods during initial orbit determination, the algorithm for approximating the uncertainty of the orbit determination results, sensor measurement errors, and nonlinear estimation and filtering methods for handling uncertainties of measurement result may influence the orbit prediction results. Simultaneously, the research emphasized that with the rapid increase in the number of space objects, traditional orbit determination methods are no longer sufficient to meet current needs in determining the orbit of space objects. There is a need for research in orbit determination algorithms with superior performance to achieve higher demand in space situational awareness [87]. Against the backdrop of rapid development in space satellite networking technology, precise orbit determination techniques for multi-satellite platforms have emerged as a new research hotspot. [PERSON] et al. proposed a dual-satellite optical orbit determination method for GEO satellites by deploying monitoring satellites on both sides of the targets. Experimental studies have shown that this method can improve the observability of targets, and the orbit determination accuracy of the target can be improved by three orders of magnitude compared to single-satellite orbit determination [88]. [PERSON] et al. conducted research on the orbit determination effects for targets in near-Earth orbits under different conditions, deploying two, four and six observation satellites. The results revealed a positive correlation between orbit determination accuracy and the number of observation satellites. However, the enhancement effect diminishes gradually as the number of observing satellites increases. Therefore, adopting a dual-satellite evenly distributed space-based target orbit determination scheme is deemed to have the highest efficiency-to-cost ratio [89]. [PERSON] et al. conducted a study on the monitoring effects of targets in GEO when deploying multiple surveillance satellites in a inclination LEO orbits.