Getting Started: Consider multiple job requirements at the beginning of the design
As the main power device of space vehicle, liquid rocket engine has full functions, high performance, great technical difficulty and long development cycle. The reusable technology of liquid rocket engine is very important for reusable space vehicle.
In the 1980s, the U.S. space shuttle program was successful and achieved the goal of partial reuse. Although the space shuttle main engine (SSME) was continuously improved, the engine was far from reaching the design goal of 55 flights in actual work. In addition, the maintenance and inspection process in the process of repeated use is complicated and the cost is high. In 2011, SSME was retired with the space shuttle. Entering the new century, the rocket vertical take-off and landing recovery technology of the US private company SpaceX has attracted attention. From the end of 2015 to the beginning of 2016, it successfully completed the recovery of the land launch site and the offshore platform, representing the latest progress in reusable vehicles.
The liquid oxygen kerosene engine is the main power unit of China’s new generation of launch vehicles, with the advantages of high performance, large thrust, non-toxic and non-polluting. From the beginning of the design of the engine, the sub-component scheme and overall layout have been demonstrated according to the requirements of multiple jobs. All valves are pneumatic, electric, hydraulic and other working forms that can work multiple times. The ground development test has achieved a single engine. Step off the stage and repeat the test drive 8 times.
During the “Thirteenth Five-Year Plan” period, our institute has carried out research on key technologies for the reuse of liquid oxygen kerosene engines in advance, and obtained a large number of theoretical and experimental research results, laying a foundation for the reuse of liquid oxygen kerosene engines.
Tackling key problems: reusing five key technologies
Due to the differences in the working environment of heaven and earth and the limitation of various guarantee conditions, the repeated ignition of the liquid oxygen kerosene engine in flight and the repeated ignition of the ground test cannot be simply equated, and the environmental conditions such as flight force and heat are also worse, so the repeated ignition of the liquid oxygen kerosene engine There are more key technical problems that need to be overcome, mainly in the following aspects:
1. Multiple ignition technology
Space vehicles that use vertical take-off and landing require the engine to have multiple ignition capabilities. For example, SpaceX’s open-cycle liquid oxygen kerosene engine Merlin-1D (Merlin-1D), during the vertical take-off and landing of Falcon 9, at most 3 ignition work is required. Second-rate.
The liquid oxygen kerosene engine adopts a combination of green and environmentally friendly propellants, which can be blown out after one ignition work to achieve repeated ignition work of the engine, and it has the ability to be reused technically. However, when the space vehicle is flying, the same guarantee conditions as the ground test cannot be achieved. At the same time, because the low temperature system needs to be pre-cooled in the ignition preparation stage of the low temperature engine, the process of the ignition preparation period is also quite different from the ground. For the supplementary combustion cycle liquid oxygen kerosene engine, these constraints will be more prominent. It is necessary to carry out technical research on the engine, optimize the pre-cooling process in the ignition preparation stage of the engine, and simplify the blow-off treatment plan after the engine is shut down and before ignition.
At present, the Chinese supplementary combustion cycle liquid oxygen kerosene engine has achieved three uninterrupted ignition starts in the ground test, and explored the blow-off treatment and pre-cooling methods in the repeated ignition work room.
2. Large-scale variable thrust technology
During the return process of the vertical take-off and landing space vehicle, due to the gradual reduction of the remaining propellant, the weight of the vehicle is getting lighter and lighter, and the engine needs to have a large-scale thrust adjustment capability in order to achieve deceleration or soft landing on the ground. In order to realize the large-scale variable thrust of the engine, it is necessary to set up adjustment elements and drive mechanisms, and at the same time, there are requirements for adjustment accuracy and adjustment rate. In addition, the large-scale changes in working conditions put forward high requirements on the adaptability of thermal components such as engine thrust chambers and main components such as turbo pumps.
The Chinese liquid oxygen kerosene engine has the stepless thrust adjustment capability, which has been fully verified by ground test vehicles. Among them, the thrust adjustment mechanism and the large-scale thrust adjustment capability have achieved flight verification on the new generation Long March 8 carrier rocket.
3. Force and thermal protection technology
Compared with single-use vehicles, reusable vehicles not only require the engine to work on the ascent section, but also re-fire the return section for vehicle deceleration or landing, especially the aerodynamic load conditions of the return section, nozzle regurgitation The heat flow conditions are more severe, and it is necessary to carry out research on the force and thermal protection technology of the engine. In addition, the interface of the non-working section that penetrates the inner cavity also needs to be protected by positive pressure or reverse sealing considering the change of the external air pressure in the return section.
The success of an aircraft test preliminarily verified the effectiveness of the liquid oxygen kerosene engine for repeated use of flight force, thermal load conditions and maintenance-free protection measures.
4. Repeated use of state assessment techniques
In order to achieve the reliability of the repeated use of the engine, it is necessary to evaluate the state of the returned engine to determine whether the engine has the ability to fly again, especially for the thermal fatigue of thermal components and the structural stress fatigue of rotor components under harsh working conditions. Research. In addition, the online real-time health diagnosis technology is developed and adopted to realize the health monitoring of the working state of the engine during the flight phase or the ballistic reconstruction of the power redundant carrier.
The domestic liquid rocket engine ground fault diagnosis system has been applied earlier in the development and test of the liquid oxygen kerosene engine, and the technology is mature. In March 2022, the actual combat application of the flight health monitoring system was realized for the first time on the new-generation Long March 6A carrier rocket. Through the research on related technologies of liquid power health diagnosis, a lot of research work has also been carried out on LOX-kerosene engine in test run or post-flight condition evaluation technology.
5. Reuse inspection and maintenance technology
In order to achieve low cost and reflect the value of the engine’s repeated use, it is required to carry out as few inspection items as possible on the returned engine, and the maintenance should be as simple as possible. , On the basis of health status assessment, the inspection and maintenance plan is simplified as much as possible, and finally the low-cost, short-cycle fast inspection and maintenance of the engine is realized.
The LOX kerosene engine has achieved a significant simplification of operation and maintenance projects through the simplified research on the use and maintenance of the launch site and the research on the related maintenance and treatment technology of repeated use.
Outlook: Gained valuable experience for full reuse
In order to realize the short-cycle processing of the engine and re-delivery the flight, the R&D team has formulated an engine inspection and maintenance plan based on the research on the technical subject of liquid oxygen kerosene engine reuse, so as to achieve short-term rapid processing and delivery of the original engine, and initially realize the liquid oxygen and kerosene engine. Kerosene engines are reused.
With the in-depth development of human space exploration, aerospace power technology has entered the stage of innovative development and large-scale development. All major aerospace powers are actively promoting the upgrading of launch vehicles, seeking to enter space quickly, reliably and at low cost. Major spaceflight countries and regions have established a relatively complete spectrum of launch vehicle types, which can meet the launch tasks of large, medium and small payloads. Major spaceflight countries have vigorously developed heavy-duty launch vehicles, in order to meet the needs of future missions such as manned moon landing, fire detection, and large-scale deep space exploration; they have continuously promoted the engineering application of reusable vehicles, and carried out key technology research and experimental verification. Based on the previous key technology verification and strong professional foundation, the next-generation rocket power products of major countries such as the United States and Russia have entered the stage of complete machine test, providing an advanced power foundation for their new space transportation vehicles.
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