A straightforward approach to construct a spacecraft transfer trajectory from the Earth to the Moon is by determining a transfer ellipse from an Earth parking orbit to an orbit around the Moon. The transfer trajectory is only the upper half of the ellipse. To get into the transfer, a large rocket burn is needed to change the spacecraft's velocity by an amount ΔV 1. To go from the transfer ellipse to an orbit around the Moon, another large rocket burn of size ΔV 2 is needed.