Abstract: Researching on the application of NRHO and DRO in the Earth-Moon system on low-energy round-trip transfer for Moon exploration, the paper combines the flyby technique and hybrid optimization technology, analyzes systematically the influence of different target orbits and different flyby azimuth on the key parameters such as flight time and fuel consumption, and provides the selection strategy for the initial value of round-trip orbit design. For the problem of initial value guess, the genetic algorithm and Lambert transfer are used to determine quickly the initial value that satisfies the constraints. Considering multiple constraints at perilune and perigee simultaneously, the fuel optimal round-trip orbit from the Earth is studied further based on the sequential quadratic programming algorithm and multiple shooting method, and the constraint equation analytic gradient is derived to improve the design efficiency. Finally, the variation characteristic of perilune attitude, transfer time and fuel consumption of different target orbits are analyzed, which is of great reference value for round-trip transfer design and parameter selection considering lunar flyby.

Key words: Lunar Exploration, Round-trip orbit, Lunar flyby, Initial value problem, Hybrid optimization