Abstract
An optimal steering law has been developed for meeting the requirements of maximizing the apse-line precession capability and the solar rotation required to attain a precession rate for GeoSail mission. The steering law takes into account all of the fundamental effects influencing the sail performance capabilities, including the shadowing effects due to the eclipse periods. A linear relationship obtained between the solar sail characteristic acceleration and the apse-line precession rate, allow evaluation of solar sail acceleration, ae necessary to perform the mission. The value of solar sail acceleration can be increased by a safety margin to compensate for the optical characteristic degradation of the sail due to a long residence in a hostile environment. The optimal steering law provide significant performance improvement with respect to simply orienting, at all time, the solar sail panel to the sun-sail line.