Abstract: To address the time-varying distribution of return opportunities and the difficulty in quantitatively evaluating long-term return support capability for spacecraft transferring from a distant retrograde orbit (DRO) in cislunar space to a geosynchronous orbit (GSO), transfer-window analysis and sustained-return constellation design are investigated. A DRO to GSO return mission model is established under Sun-Earth-Moon restricted four-body dynamics, extending conventional single-transfer trajectory design at a prescribed departure epoch to a reachability scanning problem over a long-term mission period. On this basis, multidimensional metrics for sustained return capability are developed in terms of temporal coverage, inaccessibility intervals, and coverage multiplicity. A multi-spacecraft constellation design method is then proposed by exploiting the staggered complementarity of return windows associated with different DRO phases. Numerical results show that the DRO to GSO return windows exhibit pronounced time-varying and intermittent characteristics. The inclination and direction of motion of the target orbit significantly affect the window duration, window interval, and velocity-increment distribution. Deploying multiple spacecraft with complementary DRO phases can substantially increase temporal coverage and reduce inaccessibility intervals. For multi-target return missions, joint optimization can improve the coverage of high-inclination GSO targets. The results indicate that the complementarity of return windows induced by DRO phase differences can effectively enhance sustained return capability over a long-term mission period. The proposed approach can provide a reference for emergency return of cislunar spacecraft, transfer to geosynchronous orbit service nodes, and constellation design for multi-target return support.

Key words: Distant retrograde orbit, geosynchronous orbit, orbital transfer, transfer window, reachability analysis, constellation design