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This paper proposes a prescribed-time cooperative guidance law (PTCGL) against maneuvering target with variable line-of-sight (LOS) angle constraint for leader-following missiles, where the convergence times of the state errors can be arbitrarily set. The leader missile against the maneuvering target is provided as the modified proportional navigation (MPN) guidance law. The proposed PTCGL for follower missiles consist of two parts, in LOS direction, the range-to-go (Rgo) is selected as a co-variable, avoiding the estimation of time-to-go (Tgo), and a novel second-order nonlinear consensus protocol is developed to design the PTCGL; in normal LOS direction, considering the variable LOS angle constraint, the cooperative guidance law is designed with the proposed prescribed-time sliding model control (PTSMC) method. Besides, the prescribed-time convergence of Rgo and LOS errors are proved. Finally, the effectiveness and superiority of the proposed PTCGL with leader-following strategy is illustrated by numerical simulation results.

This paper addresses the finite time prescribed performance control problem for hypersonic flight vehicle systems with abrupt actuator faults and time-varying uncertainties. The considered actuator faults contains abrupt gain faults and saltatorial bias faults, and the unknown discontinuous variations of the fault parameters are permitted. In virtue of the finite time performance functions and error transformation, the predefined tracking performance including the convergence time, the tracking error and the overshoot for the velocity and altitude can be ensured. By adaptively estimating the lower bonds of the gain faults and the upper bounds of the bias faults, the unwanted effects of the abruptly faulty actuators can be circumvented. Meanwhile, for the purpose of compensating the unknown nonlinearities, the learning-based control strategy has been employed. Finally, a number of simulation results on the hypersonic flight vehicles are conducted to demonstrate the validity of the proposed approach.

The small unmanned aerial vehicles are susceptible to wind disturbances due to the turbulent environment at their low operational altitude. Compared to conventional IMU output, the phase-advanced information provided by angular acceleration measurement is more beneficial for flight stability. This paper presents a general and systematic approach to enhance the attitude stability of small fixed-wing unmanned aerial vehicles. The methodology begins by designing a virtual angular accelerometer (VAA), which is based on 4 MEMS IMUs measurement fusion. Then, the angular acceleration is exploited to estimate and compensate disturbances. Finally, an enhanced attitude control scheme is developed to improve attitude tracking performance, where linear or nonlinear control approaches can be adopted. A VAA-based backstepping controller (BS) is designed and its stability is analyzed via Lyapunov function. Three simulation cases are carried out to verify the performance of tracking accuracy, robustness, and disturbance rejection. PID and backstepping methods are applied to the scheme. As a comparison, a widely used nonlinear disturbance observer (NDO)-based robust controller (RC) is studied. The simulation results show the excellent performance of the sensor-based VAA to observe the fast time-varying disturbance, where the NDO causes the time delay and phase lag. The tracking accuracy of the enhanced controllers (PID+VAA, BS+VAA, and RC+VAA), compared to the basic controllers, are improved by 14.3%-93.7% and the closed-loop control systems gain notable robustness.

The problem of integrated fault detection and fault tolerant control for switched systems with asynchronous switching is focused on in this paper. Based on the switched model, the inherent asynchronous switching is taken into consideration. The asynchronous switching means that the switching of filters/controllers will always lag behind the switching of modes, which will degrade the performance of the closed-loop system. The Lyapunov functional method and mode-dependent average dwell time method are combined for the analysis of the finite-time stability of the switched system. The properties of each subsystem are taken into consideration, which are less conservative. To achieve optimal performance, the filters and controllers are designed simultaneously. The parameters of filters and controllers are given in the form of linear matrix inequalities. In the end, the numerical example is given to illustrate the effectiveness of the proposed method.

This paper proposes a novel output constrained non-affine control structure by combining backstepping adaptive control with coordinate transformation technique for Generic Hypersonic Vehicles (GHVs) attitude tracking problem suffering from stochastic uncertainties. Firstly, by introducing several specific nonlinear functions, the output constrained control problem is transformed into a stabilization problem of several new variables. Then a novel adaptive control scheme that employee the boundary estimation technique and Nussbaum-type functions to counteract the effect of non-affine aerodynamic characteristics is integrated to address the attitude tracking problem. Meanwhile, two Neural Networks (NNs) are introduced to approximate and compensate the unknown nonlinearities. With the aid of a four-order Lyapunov function, the closed-loop attitude control system is proved to be stochastically stable. As a result, the output tracking errors can be guaranteed to stay in the predefined constraints during the whole control process and finally converge to an acceptable small value. Comparative simulation results are presented to demonstrate the effectiveness and advantages of the proposed control strategy.

The light field imaging produces the information on the direction of light ray, therefore the refocusing of the raw image shot with the light field camera can acquire high-resolution images of objects at different distances. This paper presents the light field image refocusing principles, rearranges raw images, transforms virtual image planes and integrates light rays, thus obtaining ideal refocused images. Then it implements frequency domain refocusing and space domain refocusing and applies the Fourier slicing theorem to implementing the frequency domain refocusing algorithm and uses the fast Fourier transform to enhance its efficiency. Through experiments, it compares the computational efficiency of the space domain refocusing algorithm and the frequency domain refocusing algorithm. It concludes that the latter has a higher computational efficiency.

The stratosail has the tensile force of the tether but no engine thrust and the size and direction of the tensile force is constantly changing. Also the changes in the size and direction of wind speed have direct influence on the aerodynamic force and spatial position of the stratosail. The establishment of the stratosail's 6-DOF models includes the modeling of a flexible tether, that of the position restriction body and that of the aerodynamic force of the stratosail, thus being a complicated flexible and rigid coupled modeling process. This paper analyzes the forces received by the stratosail and establishes its dynamics model and kinematics model under the stratosail's coordinate system. The forces include the gravity and aerodynamic force exerted on the stratosail and the tensile force and moment of the tether. According to theoretical mechanics principles, it also establishes the stratosail's mass center dynamics equation and the dynamics equation rotating around its mass center, laying the foundation for further analysis of the changes in the attitude of the stratosail and in the spatial position of its mass center.

The modeling of the stratosail of a stratospheric satellite includes both the modeling of a flexible tether and that of a rigid stratosail body, thus being a complicated and flexible-rigid coupled modeling process. This paper analyzes the stress of the stratosail and calculates the size and direction of the tensile force of the tether in different states in accordance with the moment-equilibrium principle. It analyzes the effects of the gravity, aerodynamic force and tensile force of the tether on the stratosail and calculates the inclination angle, deviation angle and tensile force of the tether at its different attitude angles. The analysis of the calculation results shows that the absolute values of the inclination angle and deviation angle of the tether increase as increasing absolute value of its yaw angle, that the lateral tensile force components of the stratosail increase but that the resultant tensile force of the tether does not increase but decreases slightly. The modeling of the stratosail of a stratospheric satellite includes both the modeling of a flexible tether and that of a rigid stratosail body, thus being a complicated and flexible-rigid coupled modeling process. This paper analyzes the stress of the stratosail and calculates the size and direction of the tensile force of the tether in different states in accordance with the moment-equilibrium principle. It analyzes the effects of the gravity, aerodynamic force and tensile force of the tether on the stratosail and calculates the inclination angle, deviation angle and tensile force of the tether at its different attitude angles. The analysis of the calculation results shows that the absolute values of the inclination angle and deviation angle of the tether increase as increasing absolute value of its yaw angle, that the lateral tensile force components of the stratosail increase but that the resultant tensile force of the tether does not increase but decreases slightly.