The motion of a spacecraft with planar solar sail, commencing from a circular geocentric orbit oriented arbitrarily with respect to the terrestrial equator, is considered. Using the small parameter method, general solutions of the equations of motion of the craft's center of mass are found, from which it follows that the perturbing force of solar ray pressure acts in a resonant mode and produces movement of the vehicle away from the earth. To within an accuracy of terms of the order of the small parameter it may be assumed that the motion occurs in the plane of the original orbit.