The space-based opportunistic positioning is an integral part of the resilient positioning, navigation, and timing (PNT) system. At the moment, most space-based opportunistic positioning terminals depend on the non-cooperative low Earth orbit (NC-LEO) satellite’s unreliable and imprecise orbit. To address this problem, this paper presents a framework for single-station two line element (TLE) estimation of non-cooperative low Earth orbit satellites. The precise TLE is obtained using Doppler observations from a single-station and the orbital parameters for constellation design. Additionally, a TLE estimation algorithm is proposed based on a genetic algorithm-ridge estimation approach with multiple initialization strategies. This method facilitates the acquisition of accurate TLE even in situations where prior orbit information is incomplete, and when the problem is ill-conditioned. Finally, real-world tests confirm that using TLEs computed using the suggested method leads to improved accuracy when compared to placement based on NORAD’s publicly available TLEs.

Using signals broadcast by a large number of non-navigation low Earth orbit satellites as navigation sources can provide positioning, navigation, and timing (PNT) services independently of global navigation satellite system (GNSS). Due to the low signal-to-noise ratio and compound orthogonal spread spectrum modulation using multiple spread spectrum codes, it is difficult to extract Doppler from the opportunity signals broadcasted by the Globalstar low Earth orbit communication constellation. Therefore, the research on Doppler positioning technology based on Globalstar opportunity signals was carried out. By analyzing the Globalstar pilot signal through measured data, the decoding method of the Globalstar pilot spread spectrum signal using square cross-term was proposed, and the decoding results were further used to extract Doppler observation by parallel code phase search acquisition algorithm. Finally, a mathematical model of coarse-time Doppler positioning was established, and the positioning was realized. The results of the experiments show that horizontal positioning performance with an accuracy of better than 100 m can be achieved by using the actual signals of two Globalstars.