Research On APT Technology For Space Multi-Node Laser Communication Networking

With the increasing demand for space information transmission,the construction of integrated information networks in heaven and earth has become an inevitable trend in the development of future communication technology.Space laser communication has become an ideal choice for building high-speed information transmission network because of its long communication distance,fast transmission rate,small size and low power consumption.The establishment and maintenance of space laser communication links rely on highperformance Acquisition,Pointing,Tracking(APT)systems,which are extremely difficult to establish under the influence of interference factors such as relative terminal motion and carrier platform vibration.Moreover,the excellent directionality of the laser beam and the small beam dispersion angle limit the signal coverage,which leads to the traditional space laser communication can only establish communication transmission with a single node,and the inability of multiple nodes to build links at the same time means that it is difficult to form a large-scale communication network,which leads to the bottleneck of the construction of integrated high-speed information transmission network in heaven and earth.In this paper,the APT technology research of space multi-node laser communication network is carried out to address the above technical difficulties.With the goal of achieving simultaneous link building of multiple nodes,the APT system pair of space multi-node laser communication network has been studied in depth from the aspects of rapid link acquisition,multi-spot detection and positioning,and stable tracking of multiple targets.With the background of space laser communication,the composition principle of space laser communication APT system is studied.Based on the in-depth analysis of the principle of traditional space laser communication APT technology,the multi-target APT system for realizing multi-node laser link networking is proposed for the problem that traditional space laser communication can only build a single node chain transmission,the optical principle of multi-node chain building is analyzed,the composition structure and working mechanism of multi-target APT system is discussed in detail,the mechanism of laser link establishment is analyzed,the laser link transmission model,studied the energy loss of each link in link transmission,analyzed the factors of link error,and analyzed the influence of APT system control accuracy on link transmission performance from the perspective of link error,providing a theoretical basis for subsequent research.To meet the demand of high probability fast acquisition of laser links between multiple nodes in space,the capture mechanism of laser links is discussed and analyzed,the gaze scan acquisition scheme based on spiral trajectory is established,the acquisition method of initial pointing angle of multi-target visual axis is given,and the pointing error is analyzed in detail,the scan acquisition model is established by improving the spiral scan trajectory,and the laser link acquisition performance under perturbation conditions is analyzed.The rapid acquisition method of laser link based on the visual axis prediction is proposed,which effectively improves the acquisition performance of the laser link while increasing the visual axis pointing accuracy.In order to meet the requirements of link error detection in multi-target tracking,we propose a multi-spot detection and positioning technology based on four-quadrant detectors,establish a spot position detection model by analyzing the working mechanism of fourquadrant detectors,propose the method of using pseudo-code sequences for beacon modulation combined with correlation detection at the receiver,realize the extraction of multi-target spot position coordinates based on a single detector under multi-beam incidence conditions,and improve the detection performance by using a nonlinear compensation optimization method for the detection nonlinearity of four-quadrant detectors.The detection nonlinearity of the four-quadrant detector is improved by using the nonlinear compensation optimization method.For the high-precision tracking requirements of laser links between multiple nodes in space,a composite loop tracking control strategy is developed in this paper.In order to suppress the apparent axis disturbance generated by platform attitude perturbation,a joint multi-beam apparent axis stabilization algorithm is proposed to achieve multi-link apparent axis stabilization based on a single inertial measurement unit by perturbation solving,and to achieve full-range link tracking,a linkage control architecture based on mirror handover is proposed with a time-dependent model for predictive targeting to ensure the smooth completion of the handover process,and to improve the composite tracking performance of the system A fine tracking Fast Steering Mirror controller based on improved Active Disturbance Rejection Control is designed,and the tracking control performance of Fast Steering Mirror under disturbance conditions is effectively improved by damping ratio adjustment and disturbance estimation optimization.After completing the above theoretical study and key link design,a prototype system is built and a series of indoor and external validation experiments are carried out.In the indoor experiments,the performance of multi-spot position detection and multi-target composite tracking is verified,and one-to-three dynamic beam tracking is realized.In the external experiments,the performance of laser link’s apparent axis pointing,dynamic capture and link tracking is verified,and one-to-two space laser communication link is successfully established and data relay transmission is realized.The experimental results have verified the feasibility of the proposed APT technology solution for space multi-node laser communication network,and solved the problem that traditional laser communication can only build a single node chain transmission,and the system performance meets the application requirements of space multi-node laser communication network.The research work in this thesis provides technical reference and theoretical support for the design and optimization of the APT system for space multi-node laser communication networking,and has reference significance for the future development of integrated multinode laser communication system,space laser communication link networking and the construction of integrated information network in heaven and earth.