Fractional-order Composite Adaptive Attitude Control of Satellite using Double Gimbal Variable Speed Control Moment Gyroscope

Satellites need constant attitude control for maintaining precise pointing while going through several external disturbance torques. In satellites, uncertainty in the inertia matrix is common due to fuel depletion and mass displacement. The estimation of these uncertain parameters while assuring the satellite attitude control is addressed in this work using a fractional-order composite adaptive control algorithm which has the attributes of the composite adaptive controller and is more robust because of its extra degree of freedom in terms of non-integer differentiation and (or) integration. A composite adaptive controller estimates the uncertain inertia parameters by utilizing both tracking and prediction errors resulting in faster convergence and reduced tracking error. A Double Gimbal Variable Speed Control Moment Gyroscope (DGVSCMG), which can produce torques in all three axes with its single unit, is used as the momentum exchange device on board. The system with the controller is stable and exponentially convergent. The efficacy of the designed controller is shown by comparing it with a direct adaptive controller and an integer order composite adaptive controller. Finally, the simulation results validate the claims made.