Abstract: In order to achieve the relay communication requirements of the Chang’E-6 lunar far side sample and return mission, a new type of sun-synchronous repeat tracking condition frozen lunar orbit and the corresponding design method are proposed. By using the von Zeipel canonical transformation method, the mean motion equations of high elliptical lunar orbits are obtained, taking into account the first and second order terms of the Earth's three-body perturbation and the J2 terms of the Moon. Based on the mean motion equation, the frozen conditions and corresponding constraint equations are established. Using the frozen condition, the conditions of the sun-synchronous frozen orbit are further proposed, and the unique advantages of this type of orbit for the lunar far-side sample and return mission are revealed. The orbit matching problem of the relay satellite with the Chang’E-6 multi-launch window is resolved. Based on the concept of nodal period of low Earth orbit, the concept of repeat tracking condition for lunar orbit is proposed, and the corresponding constraint equation is established, which realizes the repeated periodic resonance of the mission orbit period with the tracking conditions, and maintains stable track-ing conditions for a long period. Taking the design of the Chang’E-6 relay mission orbit as the background, the detailed design process and results of the lunar high elliptical relay orbit satisfying the sun-synchronous, repeated tracking and frozen condition are proposed. The high-fidelity perturbation model is used to verify the orbit design results. The simulation results show that the relay orbit elements are frozen stable, well synchronized with the sun, and the accuracy of the repeated tracking condition is high, which can achieve the requirements of the Chang’E-6 lunar far side sample return mission.

Key words: Frozen Orbit, Sun-Synchronous, Repeat Tracking Condition, Orbit Design, Relay Communication Satellite