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This paper proposes a nonsingular terminal sliding mode control scheme with fast fixed-time convergence for a class of second-order nonlinear systems in the presence of matched uncertainties and perturbations. First, based on fixed-time stability theory, a novel stable system is proposed. Then, using the fixed-time stable system, a fast fixed-time nonsingular terminal sliding surface is derived. The settling time is independent of the initial system state and can be set in advance with the design parameters; the upper-bound of convergence time is derived from the Lyapunov theory. Moreover, the proposed control scheme has an advantage in convergence rate over existing results and achieves better control performance with low control energy cost. The simulation results for a tracking system with a single inverted pendulum are presented to validate the effectiveness and superiority of the proposed control method.

In this paper, a three-dimensional (3D) impact-angle-control guidance law is proposed based on the approaches of nonsingular terminal sliding mode control and fixed-time convergence theory to intercept a maneuvering target. The guidance law is derived based on the coupled 3D engagement dynamics. To intercept the target with an expected impact angle, the nonsingular terminal sliding mode control is designed to ensure that the line-of-sight (LOS) angles and rates rapidly reach the desired values. Furthermore, the fixed-time convergence algorithm is proposed to guarantee that the LOS angles and rates are convergent in fixed time. The upper bound of the settling time can be obtained by presetting the parameters of the proposed guidance law, and it is independent of the initial conditions. The stability of the guidance system is proven via Lyapunov stability theory. The simulation results are presented to validate the efficiency and superiority of the proposed guidance law.

Disturbance-Free-Payload is a novel spacecraft architecture proposed to achieve perfect vibration isolation performance of space applications. In this paper, the object under study is a DFP system in which a flexible umbilical connection between the support module (SM) and the payload module (PM) is introduced for data, power and fluid transfer. Bead model accounting for properties of mass and flexibility, is utilized to model the flexible umbilical. With incorporation of bead model, six degree-of-freedom multibody rigid-flexible dynamics for the DFP system is established via Newtonian mechanics. Along with rotational coupling between solar panels and SM, translational coupling, in particular, is taken into consideration since there is a stringent requirement on relative position between PM and SM. Based on the accurate motion equations of the DFP system, simulation studies are conducted to gain insight of the impact of umbilical connection and translational coupling on pointing performance of the DFP system. Simulation results validate effectiveness of DFP configuration in isolating vibrations transmitted from SM to PM. Besides, umbilical connection plays an important part in degrading pointing performance of PM whereas it exerts little impact on SM. Moreover, translational coupling leads to significant pointing performance degradation for both PM and SM.