On March 29, 2022, the Long March 6A launch vehicle developed by the Shanghai Academy of Spaceflight Technology successfully made its maiden flight at the Taiyuan Satellite Launch Center. The Long March 6A launch vehicle was China’s first solid bundled rocket. It uses non-toxic and non-polluting propellants, and has a 700 km sun-synchronous orbit carrying capacity of no less than 4.5 t, which is more than 50% higher than that of a LM-4C launch vehicle. During the development of the LM-6A launch vehicle, the matching relationship between systems and the overall performance of the entire rocket improved significantly through continuous overall optimization work. This paper introduces the typical overall optimization work during the development of the LM-6A launch vehicle.

Optimal design of the tank has a significant effect on reducing the weight of a launch vehicle’s structure. In this paper, the key characteristics of a stiffened shell are dentified from the design requirements, focusing on the influence of the internal pressure on the axial compression load-bearing capacity. The computing method of the ultimate load of the stiffened shell, the parametric modeling method and the surrogate modeling technique for optimal design are reviewed. An optimization process applicable to the stiffened shell was developed and applied in the optimization work for the tanks of solid-liquid bundled launch vehicle, so a better weight reduction effect could be achieved.

Liquid bipropellant attitude control rocket engines are widely used in satellites, manned spaceships, deep space probes and other spacecraft. The performance of an attitude control engine is directly related to the lifetime, control precision and safety of a spacecraft. The study of flow characteristics of an engine transient process is important 
to improve its performance. In this paper, the transient flow test of a transparent test piece was carried out during the starting process of the attitude control engine. Then the transient process of the test piece was simulated and compared with the test results to verify the rationality of the simulation model. Transient flow simulation was carried out for the starting process of the real engine injector. The results show that the filling of the outer ring of the oxidant circuit is slower than that of the central collecting cavity, and the filling of the second layer of the outer ring is slower than that of the first layer. The filling process in the fuel path starts from the cooling hole near the inlet side and the fuel flows out in the circumferential direction. Installation direction has little influence on engine starting flow process in the ground state. 
The filling time of the engine in its vacuum state is longer than that in the ground state, the filling time of oxidizer is 31% longer than that in ground state, and the filling time of fuel is 57% longer than that in ground state.

In the industrial field, tailored blank forming with aluminum alloy (Al-alloy) has developed fast to meet the demands for large size integrated components with curved surfaces of high precision and with uniform mechanical properties. Traditional forming methods for tailored blank components faced challenges with uneven deformation behaviors and coexistence of rupture and wrinkling defects occuring during the forming process. In this paper, a new manufacturing procedure is proposed with advanced welding and forming technologies for forming integrated shell components. Friction stir welding with post-weld heat treatment was employed to prepare the tailor welded blank and improve its formability prior to forming. A double-sided pressure sheet hydroforming process was introduced to fabricate the Al-alloy tailored blank into a curved surface shell. Finite element modeling was established to analyze the effect of the weld line position and loading paths of stress distributions during the double-sided sheet hydroforming (DSHF) process. A large double-action CNC sheet hydroforming press with tonnage of 150 MN and high pressure liquid volume of 5 m3  was developed in China. As an application case of the proposed process and equipment, a full-scale tank dome with a diameter of 3 m was successfully hydroformed with a large size Al-alloy tailored blank. It was shown that the DSHF process has the advantages in controlling rupture and wrinkling defects with an Al-alloy tailored blank, and the novel manufacturing procedure enables the production of integrated thin-walled component more competitively than traditional methods.

The slug rivet is widely used in wing assembly due to its longer fatigue life and better sealing performance compared with other connection technologies. As a countersink with dual-angle is widely adopted for this type of connection, the countersink diameter and depth are key factors that affect assembly quality. Therefore, it is of great importance to efficiently inspect the countersink quality to ensure high accuracy. However, contact measurements are susceptible to the loss of accuracy due to cutting debris and lube build-up, while the hole-scanning method using laser profilometry is time consuming and complex. In this paper, a non-contact method for countersink diameter and depth measurement based on a machine vision system is proposed. The countersink diameter can be directly measured by the machine vision system, while the countersink depth is determined through the countersink diameter indirectly. First, by means of image processing technology together with an improved edge detection algorithm, the countersink diameter can be obtained. Then, a 3D microscope is employed to measure the countersink depth, which helps to model the countersink. As a result, once the countersink diameter is measured, so is the depth. The experimentation demonstrated that this method has strong easibility and enables time saving, which is conducive to improve the riveting 
efficiency.

A virtual thermal test system was built through the co-simulation using Simulink and Comsol to realize the complete virtualization of the thermal test. Using the co-simulation technology, comprehensive simulation analysis of the control system, electric field and thermal field was realized. The data state of each observation point could be directly observed at one time, including the output state information of the power amplifier, the output state information of the heater, and the thermal state information of the test unit. The virtual thermal test system has a predictive and guiding role for engineering thermal tests, and can realize thermal environment simulation beyond the existing thermal environment ground simulation capabilities, providing a basis for the development of future models.

In this paper, the properties of different low-density heat-resistant coating prescriptions were compared, and a heat-resistant coating with a density of 0.65 g/cm3, a tensile strength of 2.04 MPa, and a thermal conductivity of 0.126 W/(m·K) was obtained. The thermal performance of the coating was characterized by an oxygen-acetylene ablation test, a hot radiation test using a quartz lamp and in an arc-heated wind tunnel test. The results indicated that the low-density heat-resistant coating prescription has advantages of high temperature resistance, erosion resistance, ablative resistance and excellent heat resistance, which can satisfy the heat resistance requirements of new-generation launch vehicle fairings.
The successful application of this heat-resistant coating technology resolved the problems of low efficiency and poor adhesive performance of the traditional hand-pasted cork process, and realized the rapid spray application of the thermal protection layer, effectively improved the manufacturing efficiency and production quality of the heat-resistant layer of new-generation launch vehicle fairings.