Fixed-thrust Earth–Moon free return orbit design based on a hybrid multi-conic method of pseudo-perilune parameters

This study proposes a high-precision fixed-thrust free return orbit design method for a manned lunar mission centred on the rendezvous and docking with the lunar space station. Future manned lunar landing missions based on the lunar space station will require different spacecraft to achieve rendezvous and docking with it in different mission stages. Adopting the perilune parameters to design the Earth–Moon flight trajectory would be more convenient for decoupling in this kind of series missions. Thus, a new set of pseudo-parameters representing the perilune motion states is defined, and based on these, a hybrid multi-conic method is then proposed to design the free return orbit for manned spacecraft. The new method is more accurate than the traditional four-phase patched-conic method, and can produce initial values with a higher converging speed for a high-precision trajectory iteration design. Then, a fast and high-precision continuation method for the fixed-thrust trajectory is proposed based on the impulse-based solutions, and the gravity loss of the impulse-thrust transfer is analysed. Finally, the general characteristics and launch window of the free return orbit, as well as the reachable domain of the pseudo-perilune parameters, are analysed using the hybrid multi-conic method. The results will provide a theoretical basis for future missions planning. •New set of perilune pseudo-parameters for perilune motion states is defined.•Hybrid multi-conic method for designing free-return orbit.•High-precision fixed-thrust continuation method for impulse transformation.