Optimal Steering Law for Refractive Sails

The interaction between electromagnetic waves and matter is the working principle of photon-propelled spaceships, which extract momentum from the solar radiation to obtain a propulsive acceleration. An example is offered by solar sails, which use a thin membrane to reflect the impinging photons. Actually, the solar radiation momentum may be transferred to matter by means of various optical phenomena, such as absorption, emission, or refraction. This paper deals with the novel concept of a refractive sail, through which the Sun’s light is refracted by crossing a film made of polymeric micro-prisms. The main feature of a refractive sail is to give a large transverse thrust even when the sail is orthogonal to the Sun-probe line. Starting from the recent literature results, this paper proposes a semi-analytical thrust model that correlates the propulsive acceleration vector with the sail attitude. Such a model is then used to analyze a simplified Earth-Mars and Earth-Venus interplanetary transfer in an optimal framework.