The free-return orbit serves as the preferred orbital scheme for crewed spacecraft in earth-moon transfers, yet its design involves stringent constraints and significant initial-value dependency in existing algorithms. The earth-moon transfer trajectory planning for manned lunar exploration was addressed by proposing a dual-path neural network learning method to optimize free-return orbit initialization. A dynamic model of the free-return orbit was established to analyze the characteristics of the near-earth orbital solution space. Integrating the spatial partitioning characteristics of ascending and descending orbital phase in solution spaces, a dual-path neural network architecture designed via parameter-correlated transformation was proposed to ensure the completeness of orbital solutions. Utilizing ATK. Astromaster, the earth-moon free-return orbit planning under the dual-path network learning-based initialization method was implemented and validated through simulation. The results provide an effective reference for mitigating initial-value dependency in manned lunar mission orbit design.

The issue of the interference from the Low Earth Orbit (LEO) communication constellation to the Geostationary Earth Orbit (GEO) satellite links has become increasingly severe. Considering the impact of link interference during the design phase of LEO constellation can help mitigate this issue, this paper proposes an optimized design method for LEO communication constellation that incorporates link interference consideration. An improved interference exclusion zone is introduced and a semi-analytical interference assessment model is established to enhance computational efficiency. First, a multi-objective optimization model for LEO constellation design is established, with the constellation orbital and configuration parameters as design variables, and the LEO constellation construction cost and interference levels on GEO satellite links as objectives. Constraints include the communication coverage, ground station tracking strategy, uninterrupted communication of constellation, and configuration limitations. Second, an improved interference exclusion zone is designed, and the interference level of the constellation is evaluated using the time proportion of LEO satellites passing through this zone. Finally, the non-dominated sorting genetic algorithm is employed to solve the optimization problem. Results demonstrate that the improved interference exclusion zone can more effectively characterize harmful interference zones under different orbital altitudes and ground station distributions. The proposed time proportion metric exhibits a similarity of 0.998 with the traditional interference evaluation index while achieving a 40-fold acceleration in the computational efficiency. The optimization of the satellite phase reduces the interference level on GEO downlinks by over 5% without the additional cost, and the optimization of the constellation configuration reduces the interference level by more than 90% with a cost increase of less than one-third of the original design.

Aimed at the demand of contingency return at any time during the near-moon phase in the manned lunar landing missions, a fast calculation method for three-impulse contingency return trajectories is proposed. Firstly, a three-impulse contingency return trajectory scheme is presented by combining the Lambert transfer and maneuver at the special point. Secondly, a calculation model of three-impulse contingency return trajectories is established. Then, fast calculation methods are proposed by adopting the high-order Taylor expansion of differential algebra in the two-body trajectory dynamics model and perturbed trajectory dynamics model. Finally, the performance of the proposed methods is verified by numerical simulation. The results indicate that the fast calculation method of two-body trajectory has higher calculation efficiency compared to the semi-analytical calculation method under a certain accuracy condition. Due to its high efficiency, the characteristics of the three-impulse contingency return trajectories under different contingency scenarios are further analyzed expeditiously. These findings can be used for the design of contingency return trajectories in future manned lunar landing missions.

This paper presents an analytical model for calculating the Earth discontinuous coverage of satellite constellation with repeating ground tracks by integrating and extending the application of coverage region and route theory. Specifically, the visibility condition for a ground point is represented as a coverage region in the two-dimension map of visibility properties, and the trajectories of satellites with circular orbits and repeating ground tracks are converted to several inclined lines in the map. By analyzing the intersections of the lines and the edge of the coverage region, the coverage durations for the ground point can be calculated. Based on the point coverage, the variations of coverage characteristics along the parallel are analyzed, and the regional or global coverage characteristics of constellations can be obtained. Numerical examples show that the proposed method can accurately and rapidly calculate the coverage characteristics, e.g. revisit time and coverage time. The calculated results are extremely close to those of the Satellite Tool Kit (STK) and are also superior to the existing research results. The proposed analytical model can be a useful tool for constellation design and coverage performance analysis.