Global feedback control for attitude maneuvers of a spacecraft by two reaction wheels

The attitude control problem of a spacecraft using two reaction wheels is revisited. The angular momentum conservation constraint is used to get the reduced dynamics of the spacecraft-wheel system by directly treating the wheel speeds as control inputs. Controllability analysis shows that this reduced dynamics are locally controllable at any equilibrium if the angular momentum of the whole system is zero. Under this restriction, a singular quaternion feedback controller is first derived based on the generalized dynamic inverse method to stabilize the attitude kinematics. By introducing a novel saturated function, this controller is developed into a switched control logic to account for the singularity as well as yield bounded inputs. Then a full-state feedback is synthesized to globally reorientate the spacecraft to any desired orientation. Numerical simulation results demonstrate the effectiveness of the proposed control algorithm.