Cluster unmanned aerial vehicles (UAVs) are widely demanded. To achieve high rate and large capacity communication with cluster UAVs, one of the key but still challenge task is to perform multi-target acquisition, pointing and tracking (APT) under complex airborne environment. To solve this problem, this paper gives one composite axis APT system for multi-target laser communication with cluster UAVs. The APT system consists of a gimbal mirror and piezoelectric fast steering mirrors (FSMs), which can achieve independent and synchronous control of multiple optical axes. The cascade control scheme is designed for the gimbal mirror and the H-infinite controller is designed for the FSM. To further improve the control accuracy, the hysteresis compensator based on least square support vector machines (LS-SVM) is proposed. The pruning error minimization method of LS-SVM is applied to reduce the computational cost. The simulation studies validate the control performance of the multi-target APT system. Finally, the experimental prototype is developed. The experimental results further validate the effectiveness of the proposed multi-target APT system.

The demand for larger and lighter mechanisms for next-generation space missions necessitates using deployable structures. High-strain fiber polymer composites show considerable promise for such applications due to their exceptional strength-to-weight ratio, manufacturing versatility, packaging efficiency, and capacity for self-deployment using stored strain energy. However, a significant challenge in using composite deployable structures for space applications arises from the unavoidable extended stowage periods before they are deployed into their operational configuration in orbit. During the stowage period, the polymers within the composites experience material degradation due to their inherent viscoelastic and/or plastic properties, causing stress relaxation and accumulation of plastic strains, thereby reducing the deployment capability and resulting in issues related to recovery accuracy. This paper aims to give a state-of-the-art review of recent advances in the design, modeling, and manufacturing of high-strain composites for deployable structures in space applications, emphasizing the long-term stowage effects. This review is intended to initiate discussion of future research to enable efficient, robust, and accurate design of composite deployable structures that account for the enduring challenges posed by long-term stowage effects.

Accurate modeling and identification of the piezoelectric actuators (PAs) are increasingly demanded for intelligent micro-nano manufacturing to improve the accuracy of positioning and scanning. In this paper, one coupled fractional-order creep and hysteresis model is established only using 5 parameters. Then, the properties of the coupled fractional-order creep and hysteresis are investigated under sinusoidal and step inputs. The identification approaches are thus proposed by leveraging the special characteristics of the proposed fractional-order model. Simulation and experimental studies are carried out to validate the effectiveness of the proposed fractional-order creep and Bouc-Wen hysteresis model. Additionally, model-based inversion feedforward is implemented to validate the parameter identification. The experimental results demonstrate the effectiveness of the modeling and parameter identification approaches.

This paper investigates a whole process for the form-finding analysis of cable net reflector antennas with creep and recovery behaviors in consideration. Both the force-density and nonlinear finite element methods are extended together to establish and solve the nonlinear optimization model for the form-finding analysis. First, the equal force-density method is applied to the form-finding analysis of the initial cable net configuration, in which the creep and recovery behaviors are not taken into account. Second, the nonlinear force-density method and Schapery’s nonlinear viscoelastic theory are used to build the mathematical model of the creep and recovery behaviors of cable net reflector antennas, and the incremental-iterative method is then adopted to solve such a mathematical model. Based on aforementioned two steps, the nonlinear optimization model is established, and it is solved by the inverse iteration algorithm. Eventually, the hoop truss reflector antenna is presented as a numerical example to illustrate the efficiency of the proposed method for the form-finding design of the creep and recovery behaviors of cable net reflector antennas.