## 1 Introduction
-leveling point [44], and the autonomous navigation and timing system of cislunar detector based on DRO-LEO formation [45]. However, the above studies are mainly limited to the realization of the autonomous real-time navigation of the cooperative cislunar spacecraft, and there is still a lack of reliable means for the effective tracking and measurement of the non-cooperative targets in cislunar space. Conclusively, considering the limitations of existing space-based and ground-based cislunar space target measurement means, this research fully applies the advantages of GNSS interplanetary link signals in flexibility and reliability, with the integration of ground-based radio interferometry means, so as to achieve high-precision cislunar space target tracking and measurement. The specific exploration and verification will be introduced as follows. As one of the most significant GNSS system, China's BDS has successfully deployed ISL on BDS-3 series satellites [46]. One of the main roles of the ISL is to perform precision orbit setting and time synchronization of spacecraft [47], and the research on orbit and clock difference determination using BDS-3-measured ISL data, refinement of geometric observation models for the ISL, and modeling correction of system errors has just started [48]. The trajectory of the BeiDou satellites is shown in Figure 2. The space-division time-division access system and Ka-phase array beam shortening capability of the BeiDou ISL system exert a strong ability to expand applications [49]. The ISL system of the BeiDou-3 harbors the following features [50;51]: (i) Ka-band inter-satellite link with high ranging accuracy, strong anti-jamming capability, and good confidentiality; (ii) Space-time division multiple access and double-way ranging (Beidou-3 adopts the space-time division multiple access system, which realizes point-to-point link building between satellites); (iii) High-medium link, medium-medium link, and star-ground link mixed link construction (The Beidou-3 constellation consists of 3 GEO satellites, 3 IGSO satellites, and 24 MEO satellites, each carrying an ISL payload to realize the link construction between high-medium orbit satellites and medium-medium orbit satellites, while the ground is equipped with anchoring station equipment to realize the star-ground link building with the space constellation). Taking full advantage of the unique characteristics of satellite navigation systems as a time and space reference and global coverage, given that the BeiDou interplanetary link system is fully configurable and rapidly configurable, the user spacecraft is regarded  
Figure 2: Trajectory of the BeiDou-3 satellites (16 April 2023, 01:00 BDT). as the expansion node of the BeiDou interplanetary link system to access the BeiDou interplanetary link system and use the on-board processor to process the interplanetary measurement data to get its own orbit, which can theoretically meet the demands of real-time orbiting of cooperative and non-cooperative spacecraft in the cislunar space range [52; 53]. Based on the above analysis, this paper will utilize the inter-satellite link signal equipped on Beidou-3 satellites, combined with the ground-based CEI equipment, to achieve effective and reliable tracking measurements for non-cooperative spacecraft in cislunar space. The main contributions and structure of this paper are summarized as follows. 1. A non-cooperative cislunar space targets measurement method based on CEI and BDS-3 inter-satellite link signals is proposed, with its general scenario and specific flow discussed in Section 2. To the best of our knowledge, this is the first time the collaboration of GNSS inter-satellite link signals and interferometry-based technology has been applied in non-cooperative cislunar space target tracking and measurement. 2.