Abstract: Retro-GEO refers to the retrograde geostationary Earth orbit (GEO), which has the same or similar height as that of the GEO, but with an inclination of 180 °. A monitorsatellite on retroGEO can give early debris warning for the GEO assets every 12 hours. RetroGEO launched directly in the westward has great difficulties in ground tracking and control, as well as launch energy cost. Based on a four body model, and in order to reduce the sensitivity of design variables, a transfer to retro-GEO design model by the Moon swing by was proposed applying the trans-lunar orbital elements at the moment of perilune. The result obtanined by using orbital dynamics model continuation shows a natural property of such orbits, that is the return duration from perilune must be about 114.79 hours. The conclusion can be used to solve this kind of orbit with a high precision orbital dynamics model.

Key words: retrograde GEO, debris warning, orbit design, Moon swingby, model continuation