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A control law for retarded time-delay systems is considered, concerning infinite closed-loop spectrum assignment. An algebraic method for spectrum assignment is presented with a unique optimization algorithm for minimization of spectral abscissa and effective shaping of the chains of infinitely many closed-loop poles. Uncertainty of plant delays of a certain structure is considered in a sense of a robust simultaneous stabilization. Robust performance is achieved using mixed sensitivity design, which is incorporated into the addressed control law. [ABSTRACT FROM AUTHOR]

The attitude tracking control problem of a spacecraft nonlinear system with external disturbances and inertia uncertainties is studied. Two robust attitude tracking controllers based on finite-time second-order sliding mode control schemes are proposed to solve this problem. For the first controller, smooth super twisting control is applied to quaternion-based spacecraft-attitude-tracking maneuvers. The second controller is developed by adding linear correction terms to the first super twisting control algorithm in order to improve the dynamic performance of the closed-loop system. Both controllers are continuous and, therefore, chattering free. The concepts of a strong Lyapunov function are employed to ensure a finite-time convergence property of the proposed controllers. Theoretical analysis shows that the resulting control laws have strong robustness and disturbance attenuation ability. Numerical simulations are also given to demonstrate the performance of the proposed control laws. [ABSTRACT FROM AUTHOR]