Emre Ünal and  Hasan Başaran,  Perturbative Analysis on a Lunar Free Return Trajectory.   journal   = {International Journal of Aerospace and Mechanical Engineering}, [online]. World Academy of Science, Engineering and Technology.
    January 2021, vol. 169(1). 39 - 45
    [viewed 26 April 2024]. Available from: https://publications.waset.org/pdf/10011797.