China’s first solid-liquid bundled launch vehicle, the Long March 6A (LM-6A) successfully adopted a number of key new technologies, launching the Pujiang 2 and Tiankun 2 satellites precisely into their predetermined orbits, thus demonstrating that China has mastered solid-liquid bundled launch vehicle technology and has a new member in the new generation launch vehicle family. For the first time in China, a booster adopted a 2 m-diameter solid motor and a 270 V, 20 kW high-voltage and high-power electric servo system was used to control the swing of the solid motor nozzles. A health diagnosis system for the core first stage engine and unattended automation technology were also adopted for the first time. 

In this paper, based upon the characteristics of elastic modal combination of large solid bundled launch vehicles, the finite element theory is used to describe the complex elastic vibration of a solid bundled launch vehicle, and a new three-channel unified elastic vibration equation was established. The elastic vibration equation can reflect the coupling between channels and between boosters and core stage. Some issues need consideration in the theoretical derivation, an engineering application was proposed, and the elastic vibration model was verified. The results of the theoretical derivation and simulation show that the elastic vibration equation of a solid bundled launch vehicle established in the paper is correct and can meet the needs for the engineering application.

Compared with using liquid rocket engines, there are a lot of high-temperature solid particles in the solid-liquid bundled rocket, which make the rocket base thermal environment worse. In order to study the influence of high-temperature solid particles on the base thermal environment, firstly, the effect of particle diameter on the jet distribution and the thermal environment in a single solid motor jet was analyzed using a numerical simulation method, and the results were compared with those of a ground test. Further, the effects of high-temperature solid particles on the jet and the thermal environment of the solid-liquid bundled rocket were analyzed and compared with flight data. The results show that high-temperature solid particles can increase the jet temperature and reduce the jet velocity. The larger the particle diameter, the greater the impact on the jet core temperature. The role of high-temperature solid particles cannot be ignored in the study of the base thermal environment.

The LM-6A new generation solid-liquid strap-on launch vehicle has the structural dynamic characteristics of lower frequencies, denser modes and coupling modes in longitudinal, bending and torsion modal space. During the development phase of LM-6A, modal tests of partial stacks and the full vehicle were designed to obtain the structural dynamic properties. The structural dynamic models using the finite element method (FEM) have been verified and calibrated based on the modal test data. This paper describes the pre-test predictions and test execution, and details the comparison between the pre-test predictions and the test data. The successful maiden flight of LM-6A further confirmed the effectiveness of structural dynamic modeling and modal test for LM-6A.

The research status on the development of large segmented solid boosters is introduced, showing that the key technologies of the motor have now been acquired and meet the operational requirements of the rocket, which may provide a reference for subsequent development of large segmented solid booster motors and their application in space launchers with solid strap-on boosters.

High-power electric actuators are generally used on solid propellant motors, which further enhances the requirement on onboard supply voltage and output power of a launch vehicle. In this paper, combined with the electrical demand of China’s new generation solid-liquid bundled launch vehicle (LM-6A), high-voltage battery technology, high-power switch control technology, insulation protection technology under low pressure are studied, and the key technologies and schemes are presented. The flight test of LM-6A shows that the high-voltage power supply and distribution technology adopted is reasonable and feasible, and can be used as a reference for the designs of other launch vehicles or spacecrafts.

The 30 kW high-power electric servo system used in the solid booster of the Long March 6A (LM-6A) launch vehicle is introduced, and the function, composition of the system as well as its constituent equipments are detailed. To solve the problem of out-of-tolerance in the system dynamic characteristics, an advanced correction network algorithm architecture and double notch filter were designed. Experimental verification was conducted to prove that the dynamic characteristics requirement under multiple operating conditions could be met.

This paper investigates the servo mechanism reconfiguration and fault tolerance control issue for a launch vehicle. Firstly, the servo reconfiguration algorithm is considered as an optimization model, and commonly used optimization algorithms are analyzed and compared. An improved method based on Singular Value Decomposition (SVD) for solving the suboptimal solution of the direct assignment problem is proposed, being suitable for engineering application, while maintaining the advantages of existing algorithms. Theoretical analysis and simulation results confirm that the proposed method is able to provide the optimal reconfiguration strategy with higher computational efficiency. Finally, the numerical simulation of launch vehicle fault tolerance control fully verifies the feasibility and effectiveness of the improved method, which indicates that the method met the engineering application conditions.

According to the unattended loading requirements of the new generation launch vehicles, auto-docking technology for the first stage fill-drain connector and zero-second quick detachment technology for the second stage fill-drain connector were proposed based on the analysis and summary of unattended loading connector technology at home and abroad. These technical solutions were verified to be reasonable and feasible by tests, and they had been successfully applied to the Long March 6A (LM-6A), laying a foundation for the unattended test and launch of the new generation launch vehicles.

The maiden flight of LM-8 performed perfectly on December 22, 2020. The design concept of modularization, seriation and combination has been perfectly exhibited in LM-8. The four main technical innovations, including rapid integrated design based on modularization, engine thrust regulation, modal parameters acquisition technology based on numerical simulation, and flight load control, were verified during the maiden flight. LM-8 is now positioned to be the main force in China’s medium launch vehicles for commercial launch. In the future, the mission adaptability of LM-8 will be improved to provide efficient and low-cost launch services. In addition, new technologies to allow repeated use and autonomous flight will be validated.

Throttling of large-thrust liquid rocket engines, which can improve mission adaptability of a carrier rocket, reduce risk and facilitate rocket recovery, is a key technology for current and future space development. This paper summarizes the state of the art and trends of throttling technology for large-thrust liquid rocket engines at home and abroad. According to the working principles of propulsion for rocket engines, throttling the propellant flow rate is a major way of adjusting thrust, and regulation devices along with adjustable injectors are primary measures of throttling propellant flow rates. This paper clarifies the working principles of typical regulation devices and adjustable injectors, introduces the regulation schemes of typical large-thrust engines such as YF-100, RD-170, and SSME, and summarizes the main characteristics of current throttleable large-thrust engines. Finally, critical technologies and development trends of throttling are discussed, including combustion stability and reliable cooling of thrust chambers at low thrust levels, turbopump stability, and stable regulation and precise control in a wide range of operating conditions.

This paper introduces the autonomous control technologies for a new generation launch vehicle for guidance and attitude control. Based on the iterative guidance mode (IGM) of Long March launch vehicles, the autonomous compensation IGM (ACIGM) for the terminal attitude deviation during the coasting phase is proposed. Considering the characteristics of large static instability and weak bearing capacity, the attitude control technology based on active disturbance rejection control (ADRC) and a control method based on an accelerometer are proposed. Targeting at non-fatal failures that may occur during flights, autonomous guidance reconstruction technology, nozzle fault diagnosis and reconstruction technology in the coasting phase are studied. Some of the autonomous control technologies proposed in this paper have achieved good control results as seen through flight verification.

To meet the application requirements for a Ka-band space-based TT&C terminal for a launch vehicle, this paper proposes the implementation scheme of a space-based TT&C terminal, analyzes and solves the miniaturized design of equipment and the key technology for high-efficiency heat dissipation. The phased array antenna test shows that without external heat dissipation measures, the phased array antenna can work for a long time to meet the working requirements of launch vehicle, which has been verified in the LM-8 mission, and has wide engineering application prospects.

LM-8 inherited mature modules from other launch vehicles, adapting the overall design through the combination of engine throttling, wind compensation and load relief control, so as to reduce the aerodynamic load during flight. This paper proposes a rapid evaluation method for load relief performance, which takes launch vehicle’s characteristics, wind field, control parameters, aerodynamic deviation and structure deviation into consideration, and provides a quick estimation method for load relief performance. The load relief performance of the LM-8 launch vehicle estimated by this method achieved 10%−20% in pitch and 20%−40% in yaw. The specific results are related to parameter deviation, the altitude of wind shear and the relationship between wind direction and trajectory angle. Simulation results for a typical case with six degrees of dynamic freedom of flight proves that the comprehensive load relief performance would be between 14% to 34%, which is in line with the aforementioned method. In addition, simulation results indicate that the more severe the wind shear is, the better performance of load relief can be achieved.

LM-8 was China’s first launch vehicle which designed its dynamic characteristics without carrying out a fullscale modal test, and then in the absence of test data to establish the dynamic model. The issue was, how to accurately obtain the mode data of LM-8 with numerical simulations which directly affects the control reliability of flight. In this paper, various approaches to obtain the dynamic characteristics of LM-8 are described from the perspective of refined dynamic modeling and simulating, mode slope prediction, vertical modal test, etc. The numerical simulations were found to be in good agreement with the experimental data, and satisfied the requirements for the engineering application, which effectively supported the successful maiden flight mission of LM-8.

An electro-hydraulic actuator for the thrust vector control (TVC) of a throttlable kerolox rocket engine is introduced in this paper. The creative feature is an integrated hydraulic power drive unit, where a constant speed kerosene motor is used to draw high pressure kerosene from the engine and to drive a constant pressure variable displacement piston pump, acting as the power supply for the actuator. Its operational mechanism, to accommodate the varying pressure from the turbo-pump of a throttling engine, lies in a pressure-reducing flow regulator inserted at the motor inlet. Another key point is that the displacement of the motor is reasonably bigger than the pump so that a sufficiently wide range of pressures can be adapted. Modeling analysis and flight test results were well matched, which show the outstanding performance of this novel type actuator.

The strength of the connection structure has always been a key issue in the structural design of a launch vehicle. In this paper, the finite element analysis method is used for the strength of typical connection structures of a new launch vehicle. The research scope includes the inter-stage connection structure and the bundle connection structure. Aiming at establishing the strength of these two connection structures under flight conditions, we built a refined finite element model, simulated the bolt tensile test and obtained a calculation criteria, and carried out finite element analysis of the connection structures under flight conditions. As a result, we not only established the analysis and evaluation method of the connection structures based on the refined finite element modeling analysis, but also provided a fast numerical simulation design method for the development of the launch vehicle’s connection structures, which greatly improved the design efficiency and reduced the design risk.

Aiming at the low-frequency pressure fluctuation phenomena in certain liquid oxygen delivery systems during dual engine operation, a numerical study on the intrinsic frequency of the liquid oxygen delivery system was conducted by adopting an acoustic unit in Abaqus. Factors such as condensation characteristics of the oxygen-enriched gas gas in the liquid oxygen’s pipeline between pumps, flexibility of the accumulator, and cavitation flexibility of the engine were considered in the simulation models. The simulation results show that the second order frequency of the liquid oxygen delivery system is 8.77 Hz, and the phase difference of the corresponding acoustic modal is 180°, which is the liquid circuit frequency of the small loop between the two branches of the tee. This is consistent with the low-frequency fluctuation phenomenon during flight. Moreover, the simulation results were consistent with the liquid circuit frequency solved via the transfer matrix, which also verified the effectiveness of the frequency analysis method based on acoustic theory.

A launch pad is an important part of the launch vehicle system. It bears the weight of launch vehicles and payloads, and is burnt due to the high-temperature and high-pressure gas flow during launch. This study analyzes the development of launch pads in the world, reviews a reconfigurable mobile launch pad for multiple launchers, then proposes common points and development trends of future launch pads in the world.