Computations of Light Pressure Force and Torque Acting on the Rotor-Type Solar Sail

The algorithm for computing light-pressure force and torque acting on the rotor-type solar sail is described. The sail is composed of 16 blades fabricated from the fine light-reflective film. The shape of the film is sustained by centrifugal forces arising from the rotation of the sail about its axis of symmetry. Photons striking the film are assumed to interact with its surface in various ways. Some of them experience specular or diffuse reflection, the others are absorbed. The algorithm makes the use of computational geometry tools efficiently to take geometric properties of the sail into account in details. The surface of the sail is approximated by triangulated polyhedron. In this case computations of the force and the torque mentioned above are reduced to straightforward summing simple analytical expressions over all exposed to sunlight parts of triangle faces, the shading some faces by others were considered. The vector quantities involved have been studied as a function of the vector directed from the sail towards the Sun. In parallel with the computer based procedure there have been derived the approximate analytical expressions for these relations.