Optimal Aerodynamic Attitude Stabilization of Near-Earth Satellites

Abstract

A near-Earth satellite orbiting in the altitude range of 150 km to 450 km encounters small but non-negligible aerodynamic forces. An analysis of a system which generates sufficient aerodynamic torques to achieve active attitude control from all-moving control surfaces is presented. The satellite configuration considered has four control surfaces and the dominant gravity gradient and aerodynamic torques are included in the analysis. The equations of motion are linearized and optimal control theory concepts are applied. A feedback control system is synthesized subject to the constraint of minimum drag. Numerical studies indicate that aerodynamic surfaces of reasonable size are achievable. Damping times of the order of from a few orbits to a fraction of an orbit are possible. Nomenclature A, jB, C = moments of inertia of satellite about roll, pitch, yaw axes At = area of control surface i bi = center of pressure of 8th control surface with respect to satellite mass center d =cos9i(i= 1,2, 3) CPi, Ctj, Cot = normal force, shear force, and drag coefficients for control surface / CmA