Analysis of resonant multi-revolution Halo orbits for solar sail spacecraft in Sun–Mercury system

Mercury, as the closest planet to the Sun, experiences intense solar radiation pressure (SRP), making it an ideal target for solar-sail-based exploration. This study investigates resonant Halo orbits (RHOs) around the L1 and L2 Lagrange points in the Sun–Mercury system under the elliptic restricted three-body problem (ERTBP) with the inclusion of SRP. RHOs with resonances of 3:1, 4:1, 5:2, 6:2, and 7:2 were systematically generated, with 6:2 RHOs arising from period-doubling bifurcations of 3:1 RHOs. The continuation process involved transitioning resonant orbits from the circular restricted three-body problem (CRTBP) to the ERTBP and incrementally incorporating SRP effects. A direct collocation method replaced traditional multiple-shooting techniques to enable larger continuation steps while maintaining acceptable computational efficiency and stable convergence. Additionally, the influence of the solar sail's area-to-mass ratio on orbital geometry and stability was thoroughly analyzed. Finally, the RHOs are transitioned into quasi-Halo orbits under a high-fidelity ephemeris model to assess the feasibility for actual mission applications. Results indicate that the quasi-Halo orbits remain stable over durations ranging from 264 to 528 days. This work enhances understanding of the dynamical behavior of RHOs in the Sun–Mercury system and provides critical insights for the design of solar-sail missions for Mercury exploration.