(occupied by whoeverTF aliens or nazis)is a good example. Speed of Lunar satellites depends on lunar mass and orbital height; height and speed are easily observable by space fairing nations. If the moon is hollow, it must be made of some unlikely material of very high density. A hollow spherical shell and a solid sphere even if they've the same mass and radius, will have different moment of inertia which will show up in the secular perturbation of the rotational axis caused by other celestral bodies