On equatorial inclination of parking orbits in transfers to lunar halo orbits

This paper presents a detailed analysis on the equatorial inclination of Earth parking orbits associated with transfer trajectories to lunar libration point orbits. Orbital inclination in this work is defined with respect to the Earth's equator other than the lunar orbital plane as commonly adopted in previous works. This definition connects to the convention widely adopted in current aerospace industry, and therefore has practical meanings. By introducing a number of intermediate reference frames, an algorithm to compute the parking orbit's equatorial inclination is presented. Numerical results show that, for the same transfer trajectory designed in the autonomous framework of CR3BP (circular restricted three-body problem), the value of the equatorial inclination of the departure LEO largely depends on the choice of departure time at which the spacecraft is injected into the transfer trajectory. Two types of major periodicity, both due to the natural motion of the Moon and the Earth, are discovered to play a role in this time dependency. It is concluded that the equatorial inclination of the departure LEO can be varied by as much as 57 degrees through changing the departure times within half a month. Extensive results obtained in this work should provide good reference for the selections of both launch sites and launch windows in all missions involving Earth-Moon libration point orbits. (C) 2015 Elsevier B.V. All rights reserved.