The low orbit internet constellation represented by "Starlink" is a hot topic in the current development of the aerospace field. Multi-satellite stack technology can significantly improve the utilization rate of fairing space, thereby accelerating the construction speed of low orbit constellations, and is one of the important directions of future multi-satellite launching technology. This article analyzes the requirements and significance of multi-satellite stack technology, summarizes the existing connection forms of multi-satellite stack, and then points out the suitable connection forms for large-scale constellation construction through comparative analysis. The mature connection schemes of multi-satellite stack are interpreted, and the composition principle and technical characteristics of this technology are obtained. Finally, the difficulties and challenges in the stucture design and connection technology of multi-satellite stack are analyzed and prospects are proposed, providing reference for future multi-satellite stack structure design.

For solid-engine aircraft, closed-loop guidance methods with energy matching or angle constraints are generally used in the powered flight segment, which have high control accuracy. However, its accuracy is greatly affected by engine performance deviations. Therefore, a zero-range Orientation closed-loop guidance method based on neural network is proposed to reduce the impact of engine performance deviation on the guidance accuracy. Firstly, the motion model of the powered flight segment of the aircraft is established, and the closed-loop guidance of the zero-range Orientation is analyzed and deduced. Secondly, a multi-input neural network algorithm is designed, the input and output parameters are determined, the residual energy, the velocityto be increased and the angle of the zero-range Orientation are trained. Then, the training results of the above neural network with the zero-range Orientation closed-loop guidance are combined. This method enables feedback of different zero-range Orientation angles under different engine deviations. Finally, different deviation states for simulation verification are chosen. The simulation results show that this method can effectively reduce the influence of engine deviation on the guidance accuracy, and has strong anti-bias ability and high guidance accuracy.

In order to study the mixing and explosion characteristics of liquid oxygen and kerosene, a partial confined space test system is established to simulate the application scenarios of the launch site and the tests are carried out. It is demonstrated that when liquid oxygen and kerosene are discharged and mixed at the same time, the concentration of kerosene and oxygen increases at first and then decreases. When kerosene temperature is ${65}^{\circ}\mathrm{C}$ and ignition excitation is ${5.9}\mathrm{\;J}$, even if liquid oxygen leaks, the ignition and explosion condition are still not reached at the measuring points arranged above the liquid level. In the test when the kerosene temperature is raised to ${80}^{\circ}\mathrm{C}$, explosion occurs when liquid oxygen is released only for about 20 seconds. At ignition time, the concentration of kerosene, oxygen, and nitrogen are ${1.31}\%,{40.05}\%$ and ${58.64}\%$ respectively, and the ratio of kerosene concentration to oxygen concentration is 0.033 .

This article focuses on the dynamic model of air rudder rotation around the rudder shaft, considering a dry friction model with rotational clearance and Stribeck effect, and establishing the forced vibration equation of air rudder rotation with clearance and dry friction. The average method is applied to analyze the amplitude frequency characteristics of the rotational direction. The influence of different friction torque coefficients and external excitation frequencies on the amplitude frequency response of axial vibration is studied. The results show that when the external excitation frequency changes, the amplitude frequency curve of the vibration around the axis exhibits hysteresis nonlinear characteristics of different softness and hardness. Multiple solution frequency bands appear in the frequency domain, and the frequency domain multiple solution frequency bands increase with the increase of the friction torque coefficient.

Thermal protection is a regional protection measure covering the outer surface of the launch pad to prevent the bearing structure of the launch pad from being eroded by the rocket launch gas flow. It is a key link to ensure that the launch pad can reliably carry the rocket safely. In recent years, as the launch frequency of the conventional liquid carrier rocket represented by the Long March 2C rocket has increased year by year, the recovery time of the launch pad after the launch of the rocket has also been greatly reduced. Therefore, a rapid recovery scheme for thermal protection of the launch pad is proposed, which combines the ablation type heat protection technology with the absorption type heat protection technology, and the modular thermal protection components are designed to realize rapid replacement through simulation, test and use. The results show that the repair time of the new thermal protection is shortened from 3 days to 1 day, and the protection effect is good, which can meet the needs of high-density rocket launch.

Mobile Launcher (ML) is one of the critical ground supporting systems, which is going to be in service for Space Launch System (SLS). The function of ML includes stacking, assembly, process checkouts and launch support for the SLS rocket and Orion spacecraft. The structure layouts, operations and functions from Apollo and Saturn V are valued and baselined. The ground support equipment like umbilicals and accessories are researched and renewed. Besides, ML is aimed to be possessed of strong applicability and generality for different heavy-lift rockets, including SLS. The generality design is then performed, and modules and equipment are borrowed from previous launchers. Comprehensive tests of function, security and reliability are carried on. The research in the paper will provide reference for the launcher of heavy-lift rocket in China.

The expansion and locking process of aircraft folding rudder is a dynamic process of multi-load synthesis. The dynamic process is studied by simulation. The dynamic simulation model is established, considering aerodynamic load and friction action in the whole dynamic process. The influence of different aerodynamic load on dynamic process is analyzed by dynamically simulating the condition of obstruction, no-load and promoting aerodynamic load. By comparing the result of no-load expansion test with the simulation result of no-load condition, the accuracy of the dynamic simulation model is verified. Based on this dynamic simulation model, the friction work under different aerodynamic load condition is identified by using angular acceleration method and angular velocity method respectively from load and energy dimensions. The result of the study shows that the friction torque is affected by aerodynamic load. The friction work increases with the increase of aerodynamic promotion. The angular acceleration method and angular velocity method are both reasonable to identify the friction work. The research provides theoretical reference for engineering design and analysis of aircraft folding rudder.

In the fault-tolerant control of polyphase motors, hysteresis control is generally adopted for the more complex non-sinusoidal fault-tolerant current obtained by multi-constraint solving. Compared with hysteresis control, voltage space vector control has the advantages of low torque ripple and low energy consumption, which is more common in the control of polyphase motors. In order to solve the problem that the non-sinusoidal fault-tolerant current cannot be decoupled directly for voltage space vector control, Fourier transform is introduced and the non-sinusoidal fault-tolerant current is decomposed into fundamental current and third harmonic current to realize the decoupling transformation of the non-sinusoidal fault-tolerant current. Based on this, the decoupling transformation matrix is derived and the correctness of the processing method is verified by simulation analysis. The results show that this method can solve the problem that the non-sinusoidal fault-tolerant current under open fault-tolerant control of polyphase permanent magnet synchronous motor cannot be directly applied to voltage space vector control, so as to reduce the torque ripple and improve the motor current stability.

Modelling methods of the high-altitude wind uncertainty have significant influence on aerodynamic loads and the overall performance optimization of launch vehicles. The commonly used methods in engineering do not consider the correlation between wind speeds at different altitudes, and the simulated wind samples are inconsistent with actual wind characteristics, therefore disable to accurately predict the aerodynamic loads. A modelling method using $U/V$ wind speed components as non-stationary Gaussian processes about the height is proposed. The statistical distribution parameters of massive actual historical wind samples are analyzed, and the expansion optimal linear estimation (EOLE) method is adopted to generate wind samples with the same distribution as actual wind samples. Results indicate that the proposed method can simulate the actual wind profile more precisely than traditional methods. The simulation program of real launch vehicle is used to calculate the wind loads, and the results show that the wind loads predicted by the proposed method is far more accurate than traditional methods, which is of great significance to improve the launch efficiency and launch probability of launch vehicles.

To analyze the correlation characteristics between visible-infrared spectrum and infrared radiation of photonic crystal films, three kinds of Ge/ZnS photonic crystal films with different visible reflectance and the same infrared emissivity are designed. By simulating the infrared radiation characteristics of photonic crystal structures, the influence of solar illumination and reflection spectrum on the infrared radiation characteristics of the films in vacuum and atmospheric environments is discussed. The simulated results show that the difference of visible reflectance will lead to the discrepancy of surface temperature in the presence of sunlight. For infrared radiation, the high reflection surface will reflect solar radiation at low temperature for $3 \sim {5\mu}\mathrm{m}$ waveband, which has a negative impact on infrared camouflage. For $8 \sim {14\mu}\mathrm{m}$ waveband, when the infrared emissivity is low enough, the infrared radiation emittance of the photonic crystal structures is close. The fabrication of samples and the measurement of reflection spectrum and infrared thermography are carried out. The test results show the consistency with the simulation, and verify the infrared camouflage performance of three films. The research results are helpful to understand the visible-infrared spectrum and infrared radiation correlation characteristics of photonic crystal films, and provide reference for the spectral design and application scheme of visible-infrared camouflage materials compatible with microwave camouflage.