Abstract: A reachable domain calculation method based on interval number is proposed for the contingency return trajectories during the circumlunar flight phase. Firstly, the problem of a contingency return trajectory which adopts the non-coplanar maneuver during the circumlunar flight phase is described. The mathematics model of the reachable domain of the contingency return trajectories is established. Secondly, based on the design of the contingency return trajectory, a reachable domain calculation method of contingency return trajectories is proposed by introducing an improved interval branch and bound algorithm. Thirdly, the comparison with the traditional reachable domain calculation method based on brute force is performed in the simulations. The comparison result indicates that this method can reduce the calculation time by at least 47.4% and by at most 96.5%, and verifies the accuracy and efficiency of the proposed method. Finally, extensive simulation calculations are performed to analyze the parameter characteristic of reachable domain by using this method. The research conclusions can provide reference for the selection and decision of contingency return scheme in the future lunar exploration.

Key words: lunar exploration, contingency return trajectory, interval number, reachable domain, interval branch and bound algorithm