Numerous low-energy ballistic transfers exist between the Earth and Moon that require less fuel than conventional transfers, but require three or more months of transfer time. An entirely ballistic lunar transfer departs the Earth from a particular declination at some time in order to arrive at the Moon at a given time along a desirable approach. Maneuvers may be added to the trajectory in order to adjust the Earth departure geometry or time in order to meet mission requirements. In this article, we develop a method to determine the locations of one or two maneuvers along a transfer such that a spacecraft may depart the Earth from a fixed declination, e.g., 28.5°, at a designated time and follow a low-energy transfer to a particular lunar arrival using a minimal amount of transfer △V. One practical application of this study is to characterize the launch period for a mission that aims to launch from a particular launch site, such as Cape Canaveral, Florida, and arrive at a particular orbit at the Moon on a given date using a three-month low-energy transfer. The targeting method developed here is applied to several example transfers with varying geometries. For the purposes of this article, the transfers are designed to target halo orbits about the Earth-Moon L 2 point.
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