The optimal scheme is given for the dual-tangential transfer between two circular orbits by dual impulse method. The orbit perturbation as a result of the Earth's flattening is considered.

The Earth will return to her orbit, which is controlled by many factors, not by a single instance of perturbation by the presence of Planet X.

The orbit variation in one day under the nonspherical perturbation is shown and the motion of the orbit plane is computed.