DF-4 - Key Technical Research
Dongfeng IV is China's first two-stage liquid missile. Technically, its biggest difficulty is to break through the multi-stage rocket technology. An important technical parameter to measure the rocket is the mass ratio, that is, the ratio of the rocket takeoff mass to the rocket's empty weight. The greater the mass ratio, the greater the amount of propellant carried, the longer the rocket's flight time, and the greater the maximum speed it can reach. However, from the technical point of view, improving the mass ratio of rockets is limited. When the mass ratio of the rocket reaches a certain level, such as around 8-10, the strength and reliability of the rocket structure will be greatly reduced. On the other hand, during the continuous flight of the rocket, the propellant is constantly consumed, and the structural quality remains unchanged, and the acceleration ability of the rocket continues to decline. Taken together, the single-stage rocket cannot achieve the minimum velocity required to launch a satellite, namely the first cosmic velocity, in terms of the achievable engineering technology. For the same reason, because the maximum speed that a single-stage rocket can reach is not high, it is difficult to achieve the flight distance (range) required by a long-range missile. Therefore, both long-range missiles and launch vehicles must use multi-stage rockets.
The separation of multiple stages of rockets is very difficult. On the one hand, it is necessary to ensure that the rocket can maintain a stable attitude during separation; on the one hand, the second stage engine must achieve reliable ignition. The separation of a multi-stage rocket can neither be too early nor too late, and it is not allowed to be separated without separation. This requires its separation to be timely, accurate, reliable and safe. Usually the separation of multi-stage rocket has two methods of hot separation and cold separation.
The basic procedure of thermal separation is: at the end of the first stage of work, start the second stage engine, then shut down the first stage engine, and start the explosion to break the coupling. This separation mainly relies on the gas flow of the second-stage rocket engine to push away the first stage, and at the same time, the second stage is subjected to axial thrust before starting to ensure the reliability of starting, so the method is simple and reliable. However, the second stage will undoubtedly be greatly disturbed during the separation and consume more propellant.
Cold separation is also called deceleration separation, and its separation instruction program is generally: at the end of the first stage of work, the inter-stage coupling piece is blasted and disconnected, and then the first stage of the brake rocket or other braking device is started, and then started Rocket engine of the second stage. In this case, the inter-stage separation mechanism has fewer components and is lighter, and the working process will not be affected by large axial, lateral, vibration and other forces, and the stage separation is stable. However, this separation method requires high precision for the control system.
Dongfeng IV is China's first two-stage rocket. In order to ensure the reliability of the separation between stages, it was decided to use a more reliable thermal separation scheme. Through a series of studies and tests such as separation kinematics calculations, inter-stage aerodynamic and aerodynamic thermal calculations, and inter-stage separation wind tunnel tests and 1: 1 ground separation tests, a reasonable separation procedure is selected. At the same time, the structure adopts a diagonally drawn metal rod type interstage, which retains a large gap in the middle, so that the second-stage flame can be smoothly discharged; on the front and bottom of the first-stage propellant tank, a fiberglass insulation layer is installed , In order to prevent the gas flow of the second-level engine from burning through the front bottom of the first-level storage tank when the two levels are separated. Separate attitude control technology is also a new topic. Due to ignition first and separation later, the attitude control system cannot be switched on immediately during the separation process, leaving the missile temporarily out of control. Under the effect of separation interference, a large deviation of attitude angle may occur. In order to prevent the rudder angle from saturating during the second-stage starting control, in the channel where large separation interference may occur, the control system magnification is lower than the rated value in the first few seconds, so that the attitude of the separation stage between the stages can always remain stable, thus solving Separate state control issues.
Compared with the first-stage single-tube engine YF-1, the Dongfeng No. 4 two-stage engine YF-3 has major changes and improvements: the turbo pump is fixed on the side of the thrust chamber body; the butterfly diaphragm type pneumatic with high pressure capacity is used Valve; use small frame to transfer thrust to the bottom of the cone of the tank; for the first time, a large number of precision casting parts are used in the process to improve quality and performance. At the same time, an explosion molding process is used to produce components such as collector elbows; The extension section of the fiberglass nozzle of the ratio; the regeneration cooling partition at the head of the thrust chamber is changed to fuel cooling, so that all the oxidant flows through the body of the thrust chamber.
Since YF-3 works under near-vacuum conditions, in order to give full play to the effectiveness of high-altitude engines, a large area ratio nozzle is used, which can fully expand the gas, thereby improving the specific thrust of the engine and the chemical energy of the propellant Maximum conversion into kinetic energy of the engine. At the stage of scheme demonstration, two schemes of radiation cooling milling titanium alloy nozzle and ablated glass fiber reinforced plastic nozzle were selected. The stretched titanium alloy nozzle extension produced by the 211 Factory of the First Institute has passed the test of 6 hot test runs. However, due to the difficulty of processing titanium alloy plates, high scrap rate, and high cost, this plan was finally abandoned, and the FRP nozzle scheme was used, which was trial-produced by the Building Materials Department 251 Factory. The FRP nozzle is easy to obtain materials, low in cost, and can make the working temperature of the outer wall of the nozzle low, and the thermal impact on the instrument and the steering gear in the missile tail cabin is small. The trial production started with a low-pressure curing glass tape process. During the engine hot test run, the nozzle extension section was broken many times, resulting in the test run failure. The Institute of Materials Technology proposed a high-pressure solid process and adopted measures such as changing the resin formula and improving the production process to solve the extension problem.
YF-3 is China's first high-altitude engine, working at an altitude of more than 60 kilometers. Ensuring the smooth start of engine ignition at high altitude has become a major technical difficulty in the development work. Under the auspices of Zhang Guitian, the scientific and technical personnel of the Liquid Rocket Engine Research Institute proceeded from reality, based on the situation of spontaneous ignition of engine fuel and oxidant meeting, after research, analysis and trial and error demonstration, a solution was proposed: The same ignition environment on the ground, and further reformed the engine related system to ensure that there is a suitable time difference for the two elements to enter the combustion chamber, and adopt measures such as adhesive plugging at the throat of the combustion chamber, adding a film to the auxiliary system, etc. to ensure that when the engine starts, All channels maintain the same ignition environment as the ground. In this way, the two components of the propellant can be reliably ignited without knocking.
On March 3, 1966, the first full system test run of the YF-3 engine was successful. On October 8, the first 100-second long-distance test run was successful. In order to obtain the high-altitude performance parameters of the secondary engine, and to evaluate the high-altitude ignition and working conditions of the engine, the high-altitude environment test of the engine is required. The Liquid Rocket Engine Research Institute designed an evacuated diffusion test chamber as a high-altitude simulation test device for the engine. The engine uses flame jet evacuation to form a high-altitude and low-pressure environment in the test chamber. In September 1966, the high-altitude simulation test device was successfully developed. On November 2, the first high-altitude simulation test of the second-level engine was carried out, and the high-altitude performance parameters were obtained. The high-altitude thrust reached 290 kilonewtons, which fully met the rocket second-level engine thrust requirements. (Later increased to 320 kN). Since then, it has carried out improved design and ground test run many times, and has been tested by missile flight test, which proves that the secondary engine works reliably and the selected ignition scheme is feasible.
In order to reduce the length and structural weight of Dongfeng No. 4, the second-level storage tank adopts an advanced common-bottom storage tank scheme, and also adopts a conical bearing bottom, so that the engine thrust directly acts on the bottom of the tank. The structure of the common bottom storage tank is to prevent leakage; the second is to prevent the negative pressure on the common bottom. Because once rupture and leakage occur, the two propellants will explode when they come together. Therefore, the design must be based on the external pressure; there must be strict leak detection measures in production. The welding space of the common bottom fork ring and the shell section of the secondary box body is too narrow, and the pneumatic expansion ring can not be used to support the circle to ensure the assembly quality before welding. After repeated tests in the No. 211 Factory of the First Institute, the problem of bottom welding of the tank was solved with a special butt joint.
The First Institute of the Seventh Machinery Department also worked together with the cooperating units to solve the problem of high-speed reentry of the warhead to prevent heat. Dongfeng No.4 warhead adopts high-silica / phenolic material to mold the tip body, end cap and antenna window, and the large-area heat-resistant layer adopts high-silica / phenolic material overlapping winding and normal pressure curing process. The Nuclear Warfare Department (code 512) was developed by the Nuclear Weapons Research Institute. It is a thermonuclear warhead with an equivalent of 3 million tons and is based on the Dongfeng III warhead.
The Dongfeng-4 missile has a long range and high speed measurement accuracy requirements, especially the strict control of the safety of the test site and navigation area. The original measurement system with optical equipment as the main body can no longer meet the requirements of flight tests, and radio equipment must be established. A new measurement and control system for the main body and optical equipment.
In March 1965, according to the development test plan of the Dongfeng No. 4 missile and the Dongfeng No. 5 intercontinental missile, the Jiuquan Missile Test Base submitted an application to the National Defense Science and Technology Commission for the development of a radio ballistic measurement and test site safety system. In June, the National Defense Industry Office and the National Defense Science and Technology Commission jointly assigned the research and development tasks to the Ministry of Four Engines, code-named "154 Project". The project is led by 19 institutes of the Tenth Academy, and Wei Ming, the chief designer of the institute. The 154 project will be carried out in two phases. The first phase of the project uses a continuous-wave short-baseline interferometer for speed measurement and a single-pulse radar positioning hybrid medium-precision radio ballistic measurement system to meet the needs of the Dongfeng No. 4 missile flight test. The first-phase project includes 8 subsystems: continuous wave velocity measurement subsystem, monopulse radar positioning subsystem, guidance subsystem, time integration subsystem, safety control subsystem, on-board equipment subsystem, data transmission subsystem and radio wave propagation characteristics the study.
Under the coordination of the 154 Engineering Office of the National Defense Science and Technology Commission, the R & D and production units worked closely together to develop China ís first radio ballistic measurement system in October 1969 and participated in the Dongfeng No. 4 medium-range surface-to-ground missile in November. The first flight test. During the test, the "154" radio ballistic measurement system basically completed the ballistic measurement task, indicating that the radio measurement and control system developed by China was successful. In April 1970, the system took part in the measurement of the active segment of the launch vehicle during the launch of Dongfanghong-1 artificial earth satellite, and participated in the launch test of Dongfeng-4 several times in the future. This system, as China's early radio measurement and control system, temporarily avoided the difficult-to-solve continuous wave positioning technology in the development plan, which not only shortened the development cycle, but also helped to concentrate on breaking through phase lock, baseline cable transmission, and single pulse. Key technologies such as system application and hydraulic servo drive.
There are few external ballistic measurement parameters for missile flight. To understand the working conditions of rocket engines and control systems, it is necessary to develop telemetry technology. While developing the "154" radio measurement system, the telemetry technology for missile tests has also made great progress. The 704 Institute of the First Institute of the Seventh Machinery Department successfully developed the BWY-3 large-capacity radio telemetry system for the first time. The system has a large channel capacity and can simultaneously measure more than 100 slowly varying parameters, more than 10 rapidly varying parameters and characteristic time parameters. For the first time, the electronic exchange was used on the bomb, the magnetic recorder was used for the ground recording equipment for the first time, and the post-event data processing was quickly processed by a computer for the first time, which greatly improved the processing efficiency. In November 1969, the system participated in the first flight test of the Dongfeng 4 missile, successfully completing the tasks of receiving, demodulating, and recording telemetry signals. In the subsequent intercontinental missile flight test, it was successfully used to measure the telemetry parameters of the active stage missile.
In order to improve the reliability of telemetry warhead measurement, a variety of technical approaches have been adopted. Dongfeng No. 4 telemetry warhead adopts three methods of hard recovery, ejection recovery and medium rate radio telemetry, and all succeeded in the test process. The hard recovery technology, after repeated research and testing, uses a multi-layer composite structure hard recovery device, the tape is well protected, and the recorded parameters can be reissued.
With reference to the experience of the Dongfeng-3 large-scale test, the Dongfeng-4 missile carried out a full range of large-scale comprehensive ground tests from 1967 to 1969. In addition to the conventional full-bomb vibration and full-bomb electrical system matching test, a full-scale sloshing test was also conducted to determine the dynamic characteristics of the propellant sloshing in the tank and the damping characteristics of the anti-sloshing device. The full-bomb test and the second-level simple test were conducted 6 times. The simple test run mainly inspects the storage tank with common bottom, cone bottom scheme and power plant system scheme. The full-bomb test is a comprehensive test and evaluation of each system on the ground under a slightly more severe dynamic environment condition. Through a series of tests, a wealth of information and data were obtained, which laid a good foundation for flight tests.
Since May 31, 1966, the National Defense Science and Technology Commission, the Chinese Academy of Sciences, and the Ministry of Seven Machines have jointly agreed to launch China ís first artificial satellite launch vehicle, the Long March 1, based on a medium- and long-range missile and a third-stage solid rocket. The man-made satellite program is closely linked to medium- and long-range missiles, and is therefore highly valued by the central government. On November 23-24, 1967, the National Defense Science and Technology Commission and the National Defense Industry Office jointly decided to require the First Institute of the Seventh Ministry of Aircraft to conduct full- and long-range missile full-bomb test runs in April 1968, and conduct joint training from May to June. Experiment, and strive to launch satellites before the National Day in 1968. On January 4, 1968, the Office of the Central Committee of the Central Committee notified: The nineteenth meeting of the Central Committee of the Central Committee confirmed that Dongfeng No. 4 is an important model and cannot be abandoned or shaken. We must actively adjust our strength, make arrangements, and demand to launch the first artificial satellite in 1968.
During the critical period of Dongfeng No. 4 carrying out large-scale experiments, the scientific research work of the Seventh Machinery Department was greatly disturbed and destroyed by the "Cultural Revolution". In order to overcome the impact of the "Cultural Revolution", Zhou Enlai summoned the relevant personnel of the First Institute of the Seventh Machinery Department and the Dongfeng No. 4 full-bomb test drive on April 9, 1969, May 10, and May 10, 1969 to persevere with meticulous attention jobs. He clearly pointed out that the test drive is a matter of national honor and no one should interfere. In order to clarify responsibilities, ensure product quality, and develop according to plan, he asked the personnel who undertake the development tasks to obey the command and stick to their posts. After direct enquiries by Zhou Enlai, the first and second stage tests of Dongfeng 4 on May 19 and June 4 were successful.
On July 17, 18, 19, and 25, 1969, Zhou Enlai held consecutive meetings to resolve the ground test problems of the Long March 1 Rocket Level 2 and Level 3, and assigned Qian Xuesen to handle the test drive matters. And asked the 29 units participating in the Dongfanghong-1 satellite launch project a total of 3456 people must hold their posts and obey the command.
On July 30, 1969, the First Academy of the Seventh Ministry of the Ministry of Aeronautics proposed a group of flight test outlines for the 01 batch of Dongfeng IV. On August 22, the National Defense Science and Technology Commission approved the agreement. On August 27 of the same year, the first Dongfeng No. 4 test ejection plant was transported to Jiuquan base to prepare for flight test. The technical command responsible for the first test was Ren Xinmin. The test of Dongfeng-4 is not only related to the successful development of China's first medium and long-range missile, but also directly affects whether Changzheng-1 can successfully launch China's first artificial earth satellite. In addition, due to the increased range of Dongfeng-4, whether the missile will fly out of the country due to control system failure during the test is also a major issue to be considered. To this end, Zhou Enlai specifically listened to the report before launching, and inquired in detail about the quality of the missile and the flight safety measures taken.
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