Department of Mechanical Engineering, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran
Space Science and Technology Institute, Amirkabir University of Technology (Tehran Polytechnic), Tehran, Iran
The three-axis attitude control design based on Lyapunov stability criteria to stabilizing the spacecraft and orients it to desired attitude is presented in this paper. This attitude control system is assumed to have four reaction wheels with optimal arrangement. The reaction wheels are located in square pyramidal configuration. Control system inputs are attitude parameter in the quaternion form and the angular velocity of spacecraft and reaction wheels. The controller output is the torque required to eliminate error. In this study, actuators (reaction wheels) are modeled and required torque for attitude maneuver is converted to voltage of actuators. Armature voltage and armature current is limited to 12 volts and 3 amps respectively. Also, each wheel has an angular velocity limit to 370 rad/sec. Numerical simulations indicate that the spacecraft reaches desired attitude after 34 seconds and show the reliability of mentioned configuration with respect to actuator failure. The results show that in case of failure of one reaction wheel, the spacecraft can reach desired attitude but needs more time. Moreover, results demonstrated the controller robustness against parameter variation and disturbances. It is robust against with up to 350% change in spacecraft moment of inertia and robust against disturbance up to 0.0094 N.m that is equal 38% in comparison with the allowable reaction wheel capacity.