Abstract
An optimal steering law for sails that exploit both solar and infrared planetary radiation pressure is presented in this paper. The optimal steering law maximises the orbit raise over one revolution of the sail around the planet. An indirect analytical approach, that uses Pontryagin Minimum Principle, is used to develop specialised steering laws for the sunlit and eclipse cases in a planar motion scenario. The law for the sunlit case uses both the solar and infrared radiation emitted from the planet, while the law for the eclipse case finds the optimal sail attitude that maximises the raise of the orbit using only the planetary radiation. Numerical results show that these laws lead to better performance in terms of orbit raising against other sub-optimal and optimal strategies exploiting the solar radiation pressure only. A numerical study is also carried out to show the effects of the reflectivity coefficient in the infrared band on the orbital motion of the sail.