Anti-unwinding terminal sliding mode attitude tracking control for rigid spacecraft

In this paper, terminal sliding mode attitude tracking control without unwinding for rigid spacecraft is investigated. In order to guarantee the finite-time convergence of the system states and unwinding-free performance of the system on the sliding surface, a novel switching function is constructed by a hyperbolic sine function such that the obtained terminal sliding surface contains two equilibria. Then, a terminal attitude tracking control law is developed to ensure that the system states are driven to the sliding surface in a finite time. Moreover, a boundary layer is introduced to solve the chattering problem of the designed controller. The convergence of the system states within the boundary layer is guaranteed by imposing a constraint for the parameter of the developed switching function. Furthermore, the subsets of attraction domains of the two equilibria are given by designing a dynamic parameter for the proposed control law. The simulation results illustrate that the attitude tracking of rigid spacecraft without unwinding is realized by adopting the proposed attitude control law.