Novel Terminal Sliding Mode Based Finite Time Control Research For Spacecraft Application

Fast and precise attitude control is of critical importance for spacecraft in orbit to complete space tasks. However, it is difficult to achieve that keeping rapidity and high accuracy under control design for attitude control system, which is subject to external disturbances, control saturation lead by physical constraints of executive mechanism, and even actuator faults caused by task operation of long time and high strength. In this dissertation, finite time attitude control problem for spacecraft is investigated. A novel nonsingular saturated terminal sliding mode(NSTSM) is proposed firstly, then the focus is the design of backstepping based finite-time controller(BSFTC) for spacecraft attitude tracking in the presence of multiple constraints.Firstly, a novel NSTSM control law is investigated for rigid spacecraft attitude maneuvering, in which control input saturation and external disturbances are explicitly considered simultaneously. Specifically, in the proposed control scheme, singularity can be avoided, and also the fast convergence of spacecraft attitude maneuvering is achieved. It is important to note that the results are derived with respect to magnitude saturation and place no additional restrictions on upper bound of disturbances, and make no other small-angle assumptions. The stability analysis further shows that the controller ensures the closed-loop system can converge into the neighborhood of the sliding surface fast, and then into the neighborhood of equilibrium, with better robustness to external disturbances.Secondly, to further investigate spacecraft attitude tracking subject to external disturbances, control saturation and even actuator faults, two backstepping based finite-time control strategies are proposed. More specifically, taking into account external disturbances, a finite-time attitude tracking controller is firstly developed by introducing an integral-type sliding mode with finite time convergence, and it is further shown that the controller is independent of a prior knowledge of spacecraft inertia or boundedness of disturbances as a result. Under this, simultaneously considering control saturation and actuator fault, a finite-time fault-tolerant controller is further developed. It is interesting to note that the designed fault-tolerant controller does not require any fault detection, isolation and controller reconstruction process, and the finite time convergence of spacecraft attitude tracking can be achieved under control saturation constraint, with perfect tolerant capacity of actuator fault.Finally, numerical simulation examples for spacecraft attitude control system is involved to illustrate the feasibility and superiority using the proposed control schemes.