Nomenclature A = reference area, m a1;2;3 = characteristic optical sail coefficients B = Lambertian coefficients FXSF = transverse component of the solar radiation pressure force acting on the sail, N FZSF = normal component of the solar radiation pressure force acting on the sail, N h = offset, m k1;2 = solar radiation pressure torque coefficients P = solar radiation pressure, N∕m R = sail radius, m s = fraction of specular reflection TSRP = solar radiation pressure torque, N · m α = right ascension of the spacecraft spin axis, deg βS = solar cone angle, deg δ = declination of the spacecraft spin axis, deg e = sail’s firm emissivities η = deflection angle of the sail from the spin plane, deg ξ = torsion angle of local elements of the sail, deg ρ = reflection coefficient