Adaptive backstepping finite-time attitude tracking control of spacecraft without unwinding

This paper investigates two finite-time attitude tracking controllers for spacecraft with attitude dynamics presented by rotation matrix. With the use of rotation matrix, unwinding problem widely exists in controllers based on quaternion can be dealt with. Based on backstepping method, the first controller can be developed in the presence of external disturbance. However, the upper bound of the disturbance must be exactly known, which makes it inconvenient to implement. The second controller is constructed employing the property of hyperbolic tangent function, with which the virtual command is derived so that a finite-time convergence can be obtained. Furthermore, an adaptive law is utilized to estimate the upper bound of the disturbance online. Mathematical demonstration and simulation results validate the effectiveness of the controllers developed in this paper.