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  • A Survey of free return transits in earth-moon space

    Paper ID



    • A. J. Schwaniger


    National Aeronautics and Space Administration






    This paper presents the results of an extensive survey of free return transits which have properties that make them suitable for application to lunar exploration missions. It shows that there is a continuous region of such transits and notes that there are also other transits satisfying the definition of free return, but not in the region of transits of immediate interest for application. The method of conducting the survey was numerical and experimental. The mathematical model of the restricted three body problem was employed, and the trajectory calculations were done by Cowell’s method. Geometric notions and systematic management of the transit parameters are used to make the results of the survey more easily understood and remembered. For the purposes of this paper, a free return transit is defined as one which starts at a perigee of chosen radius from the Earth’s center, passes arbitrarily near the Moon and terminates at another perigee of radius equal to the first. Trajectories are characterized by their position and velocity components' at the close approach points to both Earth and Moon. The transits are classified hy the direction of departure from Earth and the distance of close approach to the Moon.