In order to respond to the booming development of the commercial satellite launch service market, while effectively utilizing the launching capacity of domestic satellite launch missions and the available envelope space within the payload fairing, and to provide more cost-effective launch services for satellite users, the Long March-2D launch vehicle has developed a main satellite-disk mounting configuration and a tandem-parallel-side hybrid configuration for micro satellite piggyback and multi-satellite rideshare launch missions. This has been applied in the launch missions of the Chinese Hα Solar Explorer (CHASE) and Qilu-2/3 satellites. The feasibility and efficiency of the configuration layout design have been validated through flight tests, achieving effective integration and flexible deployment of satellites with different installation methods. As a mature liquid launch vehicle of conventional propellant, the application of rideshare mode further enhances the mission adaptability of the Long March-2D launch vehicle and can reduce the launch cost of a single satellite.

In order to study the locking-swing phenomenon and swing suppression method during the pyrotechnic driving-locking process of aerocraft door, an explicit dynamic finite element simulation is conducted for an aircraft door opening-locking mechanism driven by a pyrotechnic actuator. The pyrotechnic driving-locking process of the mechanism is simulated in stages and verified compared with the pyrotechnic driving test. The locking-swing phenomenon and mechanism of the door are revealed, and swing suppression method is proposed. The research shows that the simulation method is effective, reproducing the experimental locking-swing phenomenon, and the swing angle is basically consistent with high-speed photography results. A single-freedom torsional vibration model can be used to estimate the swing characteristics of the door. Increasing the stiffness of the actuator or supported structure, or enhancing the door goose neck, has limited effect on swing suppression. Weakening the door goose neck, making it under plastic deformation during door swing, can effectively suppress the swing angle, and meet the demand for pyrotechnic opening of the door in emergency situations.

Overload changes the internal ballistics of the motor and the erosion of the thermal protection structure, which increases the coupling degree between engine design and flight trajectory design. Conventional solid rocket overall-motor discrete design is difficult to fully consider this coupling relationship. By studying the coupling relationship between internal ballistics, external ballistics and thermal protection structure, an internal ballistics model and a thermal protection structure model considering flight overload are formed. An integrated simulation method based on internal ballistic model, external ballistics model and thermal protection structure model is established to achieve accurate prediction of internal, external ballistics and thermal protection structure erosion under overload. The calculation results show that under overload, the pressure of the motor increases, the altitude and the local flight path angle of the shutdown point increases, while the flight speed remains basically unchanged. The total mass of the thermal protection structure increases and the thermal protection structure thickness of the nozzle changes, requiring strengthened thermal protection. The integrated simulation correctly predicts the changes of internal and external ballistics under overload, laying the foundation for the joint design of internal ballistics, external ballistics and thermal protection structure, which can improve the integration degree of solid rocket overall-motor design.

For the flaged structure used in the fully friction stir welded tank bulkhead of the next-generation launch vehicle, strain measurements are conducted at typical locations during the flange assembly, welding, repair welding, and hydrostatic testing processes. Additionally, finite element analysis (FEA) is performed to simulate the internal pressure loading of the tank bulkhead. The test results reveal significant non-uniform stress distribution in the flange fillet area after welding, while full stirring repair welding has a relatively small influence on the final stress level of the flange. Under internal pressure loading, the flange exhibit uneven stress distribution, leading to localized yielding at certain points. The experimental results validate the accuracy of the finite element method, demonstrating its applicability for evaluating the effectiveness of subsequent structural optimizations.

The guidance system, a core subsystem of launch vehicles, is crucial for the successful launch. Perturbation guidance, as the primary guidance method for domestic rockets within the atmosphere, relies on the design efficiency and precision of guidance parameters to determine the overall system performance. Traditionally, the parameter design is carried out by designers through extensive trial calculations and experience-based adjustments, resulting in low efficiency and high costs. To address this issue, an automatic optimization method for perturbation guidance parameters based on adjoint sensitivity and the Adam gradient descent algorithm is proposed. By constructing a point-mass dynamic model of the launch vehicle, the guidance parameter design is transformed into a constrained optimization problem. The adjoint sensitivity method is employed to efficiently compute the gradient of the objective function with respect to parameters, while the Adam algorithm adaptively adjusts the learning rate to achieve parameter auto-tuning. A two-stage launch vehicle is tested under random wind field disturbances. The perturbation guidance control parameters are optimized using a cost function that combines trajectory tracking errors and terminal range deviations. Simulation results show that the compared with the traditional manual tuning method, the proposed method can quickly find suitable control parameters. It provides an efficient and precise solution for the design of perturbation guidance parameters in launch vehicles, significantly reducing simulation time and design costs. The method also offers engineering reference value for improving the optimization efficiency of complex dynamic systems

The cryogenic coupling is the key equipment between the rocket and the ground filling system. It is mainly used for the filling, draining,venting of cryogenic propellant, such as liquid hydrogen, liquid oxygen, liquid methane, etc. The sealing reliability of the cryogenic coupling is crucial to the launch mission. According to the application characteristics of cryogenic coupling, the performance parameters and structural parameters of the metal bellows are proposed.The stiffness, strength and fatigue life of the metal bellows are obtained by theoretical calculation. The stress distribution, contact state, stiffness and residual deformation of the metal bellows at normal temperature are obtained by simulation analysis, and the influence of low temperature on the stress and stiffness of the metal bellows is analyzed. The stiffness test, life test and performance tests of the cryogenic coupling are carried out, and the test data are in good fit with theoretical calculation and simulation analysis. The feasibility of the application of the metal bellows in cryogenic couplings for the seal compensation is verified.

The rapid recovery capability of launch towers and movable launch platforms is a critical factor in determining the average annual launch capability of a launch site. The post-launch recovery situation of a space launch site for previous missions is sorted out, the content and sequence of post-launch recovery projects for previous missions are fully identified, and on the basis of which the "critical path method+ECRS analysis" method is used to analyze and optimize the post-launch recovery organization mode, workflow, equipment and facilities, and to put forward specific improvement measures and optimization plans to better improve quality and efficiency for the launch site. On the basis of this, the organizational mode of post-launch recovery, workflow, equipment and facilities are analyzed and optimized by using the "critical path method+ECRS analysis" method, and specific improvement measures and optimization plans are proposed to improve the quality and efficiency of the post-launch recovery and effectively enhance the annual launching capability of the launch site.

Movement of vehicles in the gas and liquid flow field is widely existed in the research equipment. In order to investigate the typical motion process of underwater vehicles, unsteady numerical calculation method is used to study the flow field and the active cavitation process. The calculation results show that the oscillating flow field of high or low pressure is formed in the rear edge of the vehicle in the background flow field, meanwhile the forward movement of pressure along the boundary layers significantly affects the wall pressure distribution. The active cavitations divide the flow field into the main influence zone, secondary influence zone, no influence zone and wake zone. The pressure in the main influence zone remains almost unchanged, whereas increasing in the secondary influence zone in a stepped manner. The active cavitation can eliminate the wake influence to a certain extent, making the upper and lower wall pressure changes consistent, weakening the asymmetric force of the flow field on the vehicle body and reducing the duration of negative pressure zone. Last but not least, it can also weaken the effect of water boundary layer and reduce the resistance of the whole vehicle to the lowest when developing from the shoulder to the end.

Implementing the commercial space development strategy of China, the commercial space development posture over the world is analyzed. Meanwhile, the construction demand of the launch site of the commercial space is analyzed. A conception building a LOX-methane launch site in Jiuquan Satellite Launch Center is proposed. The launch site can meet the demand of dynamical system test run, test and launch of LOX-methane launch vehicle. A conceptual design program of the LOX-methane launch site is brought forward. The program includes assorted launch vehicles, general technical indexes, basic test-launch mode, site selection, general safety, and major constructions. The demonstration shows, the conceptual design program can meet the need of launch mission, and the construction scale is moderate. The conceptual design program can fulfill the demand of the programed LOX-methane launch vehicles in China. Using the launch site, a ZQ-2 launch vehicle is flying to the space in December 2023. The above demonstration can provide referential experience for the construction of analogues commercial LOX-methane launch site in China.

Manual phase shifting operation is still the main countermeasure for single pulse radar to avoid Co-frequency Signal Interference in space launch and control missions. In order to improve the accuracy of operators' judgment of interference phenomena and the timeliness of handling during target tracking, and reduce the adverse effects of Co-frequency Signal Interference, a method based on radar target signal velocity characteristics and rocket theory flight trajectory data is proposed to analyze the motion trend of other station radar signals. Compared with the actual tracking situation, this method can accurately predict the motion trend of each radar signal under normal rocket flight conditions. Meanwhile, this method also provides a feasible approach for achieving automatic target recognition for single pulse radar in the field of aerospace measurement and control.

Magnetic integration technology is an important approach to achieve high power density because it reduces the number, volume and weight of magnetic components in power converts. A planar transformer structure and parameter design method are proposed based on matrix magnetic integration schemes for CLLLC resonant converters, such as large volume, small leakage inductance adjustment rage, etc. The structure adopts a combined winding placement method, integrating the primary and secondary resonant inductor, excitation inductor, and transformer into one magnetic component. The primary and secondary resonant inductance, excitation inductance, and transformer turn ratio adjustment and control are achieved by controlling the cross-sectional area of the magnetic core column, the combination of winding turns, and the air gap. The experimental results show that compared with discrete magnetic components, the proposed matrix magnetic integrated structure has the same function and effectively reduces the volume and weight of magnetic components, which can provide a reference for the lightweight and miniaturized design of servo power supplies.

A long-life and high-stability grease is developed to meet the demand of long-life lubrication condition with storage requirement. The physical and chemical properties,biodegradability, bearing life and rheology of the grease are studied. The results show that compared with the commercial grease, long-life and high-stability grease has lower evaporation loss at high temperature and lower oil separation ratio, which shows that it has better volatility and colloidal stability. The wear scar diameter of SRV test is smaller, and the life of wheel bearing and FE9 is longer, indicating that it has better anti-wear performance, lubrication performance and oxidation stability. The cumulative biodegradation rate in 28 days is 1.82%, which is much lower than 29.19% of the commercial grease. The rheological tests show that it has better structural stability. The developed long-life and high-stability grease has excellent comprehensive performance and can be used in the long-life application environment with long-term storage requirements and harsh working conditions.

To investigate the effects of grease degradation induced by long-term storage on the control characteristics of servo systems, the viscosity properties of the grease during storage are analyzed according to the results from the high-temperature accelerated storage test. Subsequently, the friction of the roller screw transmission is modeled to investigate the influence of lubrication degradation on the friction characteristics of servo system. Eventually, the friction models for various lubrication conditions are integrated into the servo system control simulation model to assess the impact of lubrication degradation on its performance characteristics. The obtained result is that the viscosity properties do not exhibit a clear correlation with the accelerated storage time. Selecting the degradation grease with high viscosity as the research subject, analysis indicates that the lubrication causes the increase of friction torques, the attenuation in amplitude and phase hysteresis in mid-high frequency range in servo system control characteristics. Besides, the attenuation and hysteresis aggravate as the load increases.

Jet-deflector servo-valve is known for high resistance to contamination and is widely used in aerospace where reliability is critical. However, the internal structure of jet-deflector device is very complex which makes it more challenging to a performance indication. When Computational Fluid Dynamics is introduced into an analysis of a jet-deflector servo valve, the dispersion of experimental data is always intolerable for a precise verification because of manufacturing or assembling accuracy. In this research, a distribution of experimental results is presented. After a comparison of different turbulence models, the low Reynolds number k-ε model shows more precision in pressure characteristic analysis of jet-deflector device.