Mission Design for the CubeSat OUFTI-1

CHAPTER 7.ATTITUDE CONTROL SYSTEMwhere C s is the solar constant, c the speed of light, R the reflectivityfactor, r sk the vector from the center of mass to the k’th surface elementA k , n k the outward surface normal and S the unit vector from satellite tosun.We pose R = 0.6, in a simplified scalar expression and we have:T SP,max = C sc A (1 + R) cos(i) (c SP − c GC ) = 2.06 · 10 −9 Nm (7.11)where i = 0 ◦ is incidence angle of sun and c SP − c GC = √ 0.02 2 + 0.02 2the distance between the center of mass and the center of solar pressure,projected on the surface.It’s usually cyclic when the satellite turns around the earth or arounditself (constant only for sun-oriented vehicles) and depends mainly fromthe surface properties and from the spacecraft geometry.• Aerodynamic drag: generated by the aerodynamic drag acting on the facein a point non coinciding with the gravity center.T A = 1 2 ρv2 c D∑rsk ×(n T k ˆV)ˆVAk (7.12)where c D is the drag coefficient, r sk the vector from the center of mass tothe k’th surface element A k , n k the outward surface normal, ˆV the unitvector of velocity and V the module of the velocity vector.With c D = 2 and at the perigee we have:T A = 1 2 ρv2 Ac D (c A − c GC ) = 1.84 · 10 −7 Nm (7.13)where c A the center of aerodynamic force.Variable for inertially oriented vehicle, it depends from the altitude andon the geometry.• Magnetic field: generated by the coupling between the earth magneticfield and the satellite residual dipole.T M = D × B (7.14)where B is the earth magnetic field and D the residual dipole. For themoment we are not able to estimate it.Galli Stefania 67 University of Liège