Ground- and space-based optical observation is an efficient way to catalog objects in the cislunar space. Initial orbit determination based on optical data is still an open problem for cislunar objects. The motion of these objects usually follows the law of three bodies instead of the two-body one, so current algorithms based on the two-body relation should be revised. Moreover, due to the long duration of most cislunar objects, optical observations of even hours can cover only a small fraction of one orbit, making the initial orbit determination of these objects a typical too-short-arc problem, which is difficult. A way to address this problem is to use the admissible region. In this study, an efficient algorithm constrained by the admissible region is proposed. It is easy to implement because it uses only simple iterations. Its efficiency is proven by comparing it with that of one traditional initial orbit determination algorithm.

The problem of contingency return from the low lunar orbit is studied. A novel two-maneuver indirect return strategy is proposed. By effectively using the Earth’s gravity to change the orbital plane of the transfer orbit, the second maneuver in the well-known three-maneuver return strategy can be removed, so the total delta-v is reduced. Compared with the single-maneuver direct return, our strategy has the advantage in that the re-entry epoch for the minimum delta-v cost can be advanced in time, with a minimum delta-v value similar to that of the direct return. The most obvious difference between our strategy and the traditional single- or multiple- maneuver strategies is that the complete transfer orbit is a patch between a two-body conic orbit and a three-body orbit instead of two conic orbits. Our strategy can serve as a useful option for contingency return from a low lunar orbit, especially when the delta-v constraint is stringent for a direct return and the contingency epoch is far away from the return window.