Integrated power and attitude control of spacecraft using variable speed control moment gyros

A globally asymptotically stable control law for attitude tracking is designed for a rigid body spacecraft with variable speed control moment gyros (VSCMG) as attitude control actuator. The angular velocities of gimbals and the angular accelerations of rotors are treated as a control input vector in the steering law design. A weighting minimum norm solution is applied to determine the attitude control vector of the VSCMG, while an input vector which is orthogonal to the attitude control vector is used to store/release energy based on given power. A hybrid cost function symbolizing both control moment gyros singularity and wheel speed equalization is constructed. For a redundant system, the null motion of the VSCMG is designed using the gradient method based on the hybrid cost function. The null motion is employed to avoid the singularity in control moment gyros mode, and reduce the possibility of rotor speed saturation and VSCMG zero singularity due to large differences among the rotor spin rates. The energy storage power during sunlight is programmed using kinetic energy feedback to keep long-term energy balance. Numerical simulation results based on a sun-synchronous satellite demonstrate the validity of the system.