A procedure for the estimation of solar radiation torque components considering multiple shadow regions and surface reflectance properties

Abstract

The estimation of solar radiation torque components acting on a spacecraft requires modelling of surface geometries along with their reflectance properties and shadow regions. This paper details a procedure for the computation of the effective area and the centre of pressure on surface elements, considering the shadows cast by various appendages. A set of edge coherence properties are used to obtain the vertex points of the shadow regions. Multiple shadow regions with overlapping sections are replaced by equivalent circular patches for fast computation of the combined area and centroid. The surface parameters for the effective area exposed to solar radiation, together with the surface normal direction, yield the force and torque components on each element in a sun-oriented reference frame. The torque vector in the body-fixed reference system is obtained using the transformation involving the relative attitude of the spacecraft with respect to the sun direction.