Abstract A near rectilinear halo orbit (NRHO) is regarded as a potential orbit for a future deep space station that can effectively support sustainable crewed lunar exploration missions. In this paper, the L2 southern NRHOs are selected as the research object, and a direct transfer trajectory from an NRHO to a low lunar orbit (LLO) is designed and analyzed. First, based on the circular restricted three-body problem, the characteristics of NRHOs are discussed including geometric behaviour, stability and synodic resonance. Second, optimal direct transfer trajectories are obtained by combining a local gradient optimization with a numerical continuation strategy. A reachable domain calculation model is established. Finally, simulations are carried out to verify the feasibility of the trajectory design method. The relationship between the velocity change and the reachable domain is further analysed through simulation calculations.

中文翻译：

---

近直线晕轨道至低月轨道直接转移轨迹设计与分析

摘要 近直线光环轨道（NRHO）被认为是未来深空站的潜在轨道，可以有效支持可持续的载人月球探测任务。本文以 L2 南部 NRHO 为研究对象，设计并分析了从 NRHO 到低月球轨道 (LLO) 的直接转移轨迹。首先，基于圆形受限三体问题，讨论了 NRHO 的特性，包括几何行为、稳定性和会合共振。其次，通过将局部梯度优化与数值连续策略相结合，获得最佳直接转移轨迹。建立可达域计算模型。最后通过仿真验证了轨迹设计方法的可行性。