Abstract
Rapid attitude maneuvering and high pointing accuracy are two keywords for advanced missions of next generation satellites. The single-gimbal control moment gyro (CMG) is regarded as an ideal torque generator for rapid maneuvering due to its torque amplification capability. However, singularities, unknown friction effects and its real steering resolution constrain its practical performance. This paper presents a robust attitude control approach based on variable-structure theory with a time-varying sliding surface. This approach guarantees minimum angular path maneuvering, global stability and asymptotic convergence in the presence of CMG practical restrictions, inertial uncertainties and various disturbances. By taking CMG gimbal friction as unmodeled disturbances, the approach is independent of the gimbal friction model. Furthermore, a magnetic compensation method with gimbal rate feedback is proposed to reduce torque-generated error caused by the CMG steering mechanism including singularity avoidance logic and steering resolution limits. This method also attenuates the frequent switching operation of the CMG during the stabilization phase. Numerical simulations demonstrate the validity and feasibility of the proposed approach. It is also shown that the magnetic compensation method does not only improve the tracking accuracy effectively, but also reduces the total power consumption, which is very desirable in practice.
