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.

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.

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.