In order to solve the problem of vulnerability of the missile-loaded motor shaft and bearing in the high overload environment of 23 000g guided artillery projectile, the anti-high overload brushless DC motor using a combination of disc spring and special steel ball for buffering and vibration damping is designed. Firstly, the acceleration load curve of the missile-borne motor is obtained by calculation. The bearing and shaft of the brushless DC motor are analyzed to be the failure prone parts. Secondly, according to the energy absorption characteristics of dish spring and steel ball, a composite damping structure of brushless DC motor combining dish spring and special steel ball is designed in the case of limited structural space. And based on this structure, a high speed and fast response anti-high overload motor is designed. Finally, the simulation and experimental analysis of the designed motor show that the design of the composite buffer structure can effectively reduce the stress and deformation of the motor shafting parts under the high overload environment. The structure of the anti-high overload motor has no obvious damage after the Marshall's drop hammer test, and the working performance meets the requirements of precision guidance control.

As the key interface between launch vehicle and ground support equipment, the cryogenic connector is used for filling and venting of cryogenic propellant, and it falls off before or after launch. Affected by the high temperature and high humidity environment of Hainan launch site, the low temperature surface of the rocket-ground interface is more prone to frost and ice after long-time filling, which hinders the action of the separation and increases the resistance of the connector to fall off. Quality problems affecting the launch process occurred in historical missions. An improved scheme for the rocket-ground interface is proposed, which can reduce or avoid icing at the unlocking part and reduce unlocking resistance through thermal design optimization.

The intelligent upgrade of the aircraft has put forward new requirements for guidance capabilities, and traditional algorithms perform poorly in tracking spatial three-dimensional trajectories under biased conditions. An aircraft trajectory tracking guidance method is designed based on the TD3 reinforcement learning algorithm. Through the action space in the form of deviation, the penalty term in the reward function and the guidance of the rate of change of distance, problems such as difficult convergence of algorithm training, large fluctuations in control quantity, and large cumulative deviation at the middle and final shift points are solved. Compared with the traditional LQR algorithm, the reinforcement learning guidance algorithm has significantly improved guidance accuracy and deviation adaptability, and has good versatility, which can be applied to small-scale formation maintenance issues.

To ensure the reliability of dynamic seal performance of low temperature valve in liquid rocket engine, the sealing pressure and performance of a new type of labyrinth packing dynamic seal structure are simulated and tested. Firstly, the structure of traditional packing dynamic seal is optimized, and a new PTFE-Graphite-Metal labyrinth composite seal is designed. Then, based on the thermal stress coupling method, the influence of the working condition on the dynamic sealing performance is analyzed, and two empirical models for PTFE and Graphite are proposed to represent the dependence of contact stress on both the loading pressure and temperature. Finally, the sealing performance of the new labyrinth dynamic seal is tested at room and low temperature. The results show that the new labyrinth dynamic seal can achieve good sealing performance at room and low temperature, which is consistent with the simulation results.

To address the issues of penetration and precision attacking for air-to-air missiles, an analytical solution for the miss distance of a non-zero-order guidance system is derived. The solution is then extended to advanced guidance laws beyond proportional navigation guidance. Based on these results, the effectiveness of evasion under different maneuvering strategies is analyzed which theoretically explaining the typical characteristics of miss distances in step and serpentine maneuvers and factors influencing the optimal maneuvering strategy are studied. Through reasonable adjustment of maneuver timing and direction, the effectiveness of evasion is improved. Furthermore, considering the integration of penetration and attacking through intelligent guidance laws, an adaptive-stepsize sparsified sampling prior model theory infusion remedial training agent learning (ASTRAL) is introduced. Simulation results show that the missile agent trained with the ASTRAL can effectively evade defender while maintaining its attacking capability during penetration. In addition, the generated guidance law demonstrates good engineering feasibility.

This study investigates the combustion performance of gas-oxygen and gas-methane pintle injectors, which discusses the influence of pintle injector structure design parameters and thrust chamber combustion design parameters on the combustion performance. Theoretical analysis is carried out by numerical simulation and other methods. The simulation results show that the oxidizer central pintle injector has a higher combustion performance. A larger angle of the pintle head and a smaller distance of the intermediate sleeve have a higher combustion performance. A smaller pintle head radius can significantly play a role in cooling the pintle head, but there is a certain loss of combustion performance. When the speed ratio is about 1.1, the combustion performance is higher, and the temperature of the pintle head is lower. When the mixing ratio of oxygen and methane is around 3, the combustion performance is higher.

During the flight of aircraft, a coupling effect between the fluid aerodynamic forces and the structural elastomer will be formed, and this interaction may cause different degrees of damage to the divergence and jitter of the elastomer, resulting in safety risks. A numerical simulation method of fluid-structure coupling based on time-space conserved element solution and immersion boundary is proposed. The method of time-space conserved element solution is used to calculate the fluid domain, and the submerged body-fitted mesh boundary method is used to identify the fluid-structure coupling boundary surface. Taking NACA0018 as an example, the cloud image of wing outflow field pressure and velocity at different angles of attack is obtained through simulation data. At the same time, the buffeting amplitude of the wing under different inlet velocity and its rule are studied. The research shows that the fluid-structure coupling method has high accuracy and stability in solving high-speed compressible flows with complex flow patterns, including shock wave or detonation and large deformation problems, providing a reference research method for related research.

Bistatic radar is widely used in military field by virtue of its good anti-jamming ability and accurate detection and identification ability, and how to effectively jam this transceiver-split radar system has become a current research hotspot. Typical jammers have large fluctuations of bistatic RCS with angle change and weak bistatic scattering strength, which are not advantageous in countering bistatic radar. Therefore, a new type of combined jammer against bistatic radar is proposed by analyzing the bistatic scattering characteristics of four types of typical jammers. Afterwards, electromagnetic simulation calculations are carried out on the new combined jammer monomer/array of different bands, sizes and spacings to study the bistatic scattering characteristics under different parameters, and compared with typical jammers. The results show that the new combined jammer monomer/array has strong bistatic scattering strength and the fluctuation amplitude of its RCS with respect to angle is smaller, with good bistatic scattering characteristics, providing technical support for effectively jamming of bistatic radar.

When the design input is limited during the initial stage of scheme argumentation, in order to solve the problem of how to conduct control capability analysis quickly and effectively, the adaptability of traditional control capability analysis method is analyzed. A set of controllability analytical method for reentrant launch vehicles is researched by dynamic modeling and original method improving. And under the premise of limited control capability, the constraint conditions for allowable flight conditions is limited preliminary in order to quickly locate and feedback the closure of the overall unit control capability.

A 5B70 aluminum alloy sheet with ${1.5}\mathrm{\;{mm}}$ thickness is welded by tungsten inert gas (TIG) welding with 5B71 filler wire. The micro-structure evolution and refinement characteristics of the welded joints are investigated. The research results indicated that weld joints with excellent formation can be obtained by adopting reasonable welding parameters. The internal structure of the weld seam shows that the weld zone is mainly composed of equiaxed crystals forming a cast structure, the size of the grain structure is uneven, there are widely larger grains with a diameter of ${40}\sim {50\mu}\mathrm{m}$, as well as ultrafine grain areas with a diameter of about ${20\mu }\mathrm{m}$ which distributes in fine strips and small blocks. The area of the ultrafine grain region is obviously smaller than other areas. It mainly distributes in the direction parallel to the fusion line, with a few distributed on the weld surface. Sc and Zr were used as modificator to refine the grains. The ${\mathrm{{Al}}}_{3}\left({\mathrm{{Sc}},\mathrm{{Zr}}}\right)$ second phase particles are precipitated in the welding pool during solidification. The function of such particle is to form heterogeneous nucleation particles, reduce nucleation power and increase the number of crystal nuclei. The area where Sc elements are enriched had a higher degree of grain refinement. The “undercooling” zone is formed along the front of the solid-liquid boundary, which promotes the formation of equiaxed grains. It results in a higher degree of grain refinement, which size is only about one half of other zones.