Diagnosing Inclination-focused Effects on the Short-term Earth--Moon Transfer Dynamics

Abstract Context: Trajectory optimisation for Earth-Moon transfers is commonly approached using reduced-dimensional assumptions where orbital inclination is taken as a secondary or passive parameter adjusted in the planar optimisation. While this approach is acceptable and more effective for the initial mission planning, its implications and effects in the optimisation and solution accessibility are not fully regarded as a primary topic and thus understood. Aims: This exploratory study aims to investigate the role of orbital inclination as an active variable in short-duration Earth-Moon transfer optimisations to assess how inclination-focused coupling influences solution accessibility focusing on the Earth-departure to lunar flyby phase. Methods: Multi-epoch short-term transfer analysis is conducted using European Space Agency's open-access trajectory optimisation tool as a two-stage numerical optimisation tool in which the departure inclination as a primary variable is systematically varied while other orbital elements are held fixed. Optimised transfers are analysed using the \((\Delta v)\) performances and feasible numbers derived from the repeated optimisation runs. The robustness of the feasible solutions is used as a proxy to investigate structured sensitivity in the local optimisation map rather than as a direct signal of long-term dynamical stability. Conclusion: The results show that a non-monotonic dependence of optimisation performance and robustness on the departure inclination with a decrease in solution robustness beyond \((i\approx40^\circ)\). In this regime, optimised solutions show increased sensitivity to initial conditions indicating that inclination actively reshapes the local optimisation landscape over short transfer durations.These findings suggest that inclination cannot always be treated as a passive geometric variable in short-duration Earth-Moon transfer. The study highlights optimisation robustness as a useful diagnostic for identifying structural sensitivity based on the optimisation setup and motivates greater care in the treatment of inclination in three-dimensional transfer problems.