Ride more comfortable, docking more calmly, more accurate measurement and control
Hardcore Technology Guardianship
At 0:23 a.m. on October 16, a dazzling golden light passed over the desert moonlight. Three astronauts Zhai Zhigang, Wang Yaping and Ye Guangfu boarded the Shenzhou 13 spacecraft on the Long March 2 F Yao 13 carrier rocket ( (Hereinafter referred to as "Chang Er F Rocket") drive to the Xinghai and stay in the "Tiangong".
From the launch of the rocket to the successful docking of the spacecraft to the core module, to the smooth stationing of the astronauts, how does Shenzhou 13 pass through?
What are the "heritors" behind it to escort it?
The reporter will take you to understand those hard-core technologies that escort Shenzhou Feitian Road——
1 From turbulence and vibration to double comfort, the astronaut rocket "special train" is upgraded again
Shenzhou 13 was launched into space, accompanied by a huge rocket tail flame and roar. We can see from the live broadcast that the expressions of the three astronauts seem to be the same as those on the ground, and there is no obvious shaking.
In sharp contrast, during the Shenzhou 5 manned mission, when the rocket flew to an altitude of thirty to forty kilometers, the rocket and the spacecraft vibrated sharply and resonated, causing Yang Liwei to endure great discomfort.
Later, Yang Liwei recalled the "unbearable" 26 seconds in "A Day in Space": "The painful feeling is getting stronger and stronger, and the internal organs seem to be broken. I can hardly bear it and feel that I am going to die."
"This very uncomfortable resonance was once a world-class space launch problem." Chang Wuquan, the chief designer of China Aerospace Science and Technology Corporation, the first director of the second F rocket, told reporters that as early as the 1960s, the United States launched Hercules. During the rocket process, there was a vibration that lasted 30 seconds; the French rocket had also experienced similar problems, which affected the life of the satellite.
How to make these 26 seconds no longer "unbearable"?
After calculation and analysis, the testers believe that the "root disease" may be in the oxidizer: when the vibration frequency of the fuel in the oxidizer is close to the vibration frequency of the rocket structure, divergent vibrations coupled between the structure and the liquid are likely to occur.
After experimental analysis, the conclusion confirmed the previous speculation: the problem lies in the rocket’s POGO vibration (longitudinal coupled vibration).
After finding the root cause of the problem, the Changer F rocket development team set out to improve the rocket's performance.
First of all, the developers reduced the magnitude and time of vibration by reducing the bellows on the rocket booster accumulator, but the vibration problem has not been completely solved; the development team optimized the design again and changed the booster accumulator to a variable Energy accumulator.
This device can absorb the energy generated when the fuel vibrates and change the vibration frequency of the fuel.
The vibration frequency of the fuel and the vibration frequency of the rocket structure are no longer close, so the rocket will not produce POGO vibration.
As a "special train" for astronauts, safety performance is undoubtedly the first.
The Chang-2F rocket is China's first launch vehicle with clear 0.997 safety index requirements.
The safety index indicates the conditional probability that the astronauts can return safely when the rocket fails; the 0.997 safety index, that is, assuming 1000 failures during launch, only 3 unsuccessful rescue measures are allowed.
In the pursuit of safety, the rocket development team does not stop.
Entering the space station mission phase, the Chang-2F rocket has carried out more than 100 technical status changes, of which more than 70 are related to the improvement of reliability.
These improvements do not involve major technological changes, and the main purpose is to eliminate weak links.
For example, in view of the risk of engine ignition failure, the diameter of the fire hole of the main engine was changed from 4 mm to 6 mm to further improve ignition reliability; according to different positions, more precise angle design requirements for the injection port of the thrust chamber of the engine's secondary traveling engine were proposed. , So that the propellant can be more fully fused and burned, and provide strong power for the rocket.
Unlike other types of rockets, the Changer F rocket has an elongated "lightning rod" on the top-an escape system.
If the rocket has an unexpected situation, the escape vehicle will take the return capsule and fly away from the failed rocket like a "carrot".
But in the process of opening the parachute, the return capsule will be greatly affected by the low-level wind on the ground.
Previously, escaping aircraft could only escape in a fixed direction, posing a safety risk.
"If the escape vehicle can only escape eastward, it happens that a westward wind blows from the ground. In this way, when the return module is in an open parachute state, it is likely to be blown back to the vicinity of the malfunctioning rocket, and the astronauts will be in danger. ." said Liu Feng, deputy chief of Changer F Rocket.
In order to ensure the safety of astronauts, developers have improved the Chang-2F rocket's escape and safety control system to improve the security and anti-jamming performance.
On the basis of the existing control escape engine, the developers added the engine ignition function, so that the escape aircraft can escape in the direction perpendicular to the ground wind, which is safer and more flexible.
"For example, the ground is blowing from the north and south wind, now the escape ability is improved, you can choose the direction perpendicular to the south and north wind to escape in advance to avoid the ground wind." Chang Wuquan said.
After the escape system is improved, the evaluation value of the safety index of the Chang-2F rocket has reached the international advanced level of 0.99996.
That is, after launching 100,000 times, there will be 4 escape failures.
2 Shenzhou docked at the space station radially for the first time, technological innovation made the docking more accurate and stable
At 6:56 on October 16th, the Shenzhou 13 manned spacecraft successfully docked to the radial port of the Tianhe core module using the autonomous rapid rendezvous and docking mode, together with the previously docked Tianzhou-2 and Tianzhou-3 cargo spacecraft It forms a four-cabin (ship) combination, and the entire rendezvous and docking process lasts about 6.5 hours.
From Shenzhou 8 to Shenzhou 12, the five spacecrafts are all docked axially (forward and backward).
This is the first time that the Shenzhou spacecraft has docked at the space station radially, that is, the spacecraft and the core cabin are radially docked at the interface.
When docking, the core cabin and the spacecraft are in a vertical state.
Why does the Shenzhou spacecraft carry out a radial rendezvous and docking with the space station?
"Because there will be astronaut crew rotation in the later period, and there will be two spacecraft docking with the space station. The radial rendezvous and docking can improve the channels and means of entering the space station." Sun Jun, the chief task officer of the space station of the Beijing Aerospace Flight Control Center, said that the engine of the Shenzhou spacecraft , Control systems and sensors are all designed specifically for docking with the space station in all directions, and only the Shenzhou spacecraft can perform radial rendezvous and docking with the space station.
The radial and axial directions are perpendicular to each other, and the direction is changed by 90 degrees, which greatly increases the difficulty of docking.
Gao Xu, deputy chief designer of the spacecraft model system of the General Design Department of the Fifth Academy of China Aerospace Science and Technology Corporation, told reporters that there are "trilemmas" in radial rendezvous and docking, which also makes the space waltz more exciting.
It is difficult to continuously control the attitude and orbit.
When the forward and backward rendezvous and docking, the spacecraft has a 200-meter holding point, even if the engine is not working, the spacecraft can maintain a stable attitude and orbit for a long time.
Radial rendezvous does not have a stable midway anchor point. It is necessary to continuously control the attitude and orbit of the spacecraft, which consumes a lot of propellant and makes troubleshooting difficult.
It is difficult to determine the attitude and relative position.
The spacecraft is equipped with sensors, just like the eyes of the spacecraft.
During the radial rendezvous process, the spacecraft must perform a wide range of attitude maneuvers from horizontal to vertical flying, so higher requirements are put forward for the "eyes" to identify targets and not be disturbed by complex illumination changes.
The difficulty lies in the manual rendezvous mode of the astronauts.
During the radial rendezvous and docking process, the most familiar reference datum of the earth basically fails, the measurement and control conditions become worse, and the relative dynamic motion characteristics are different from the forward and backward rendezvous, which increases the operation of the astronauts in the manual rendezvous mode. Difficulty.
The successful implementation of the first radial rendezvous and docking is inseparable from the technical research and ground experiments of the Shenzhou spacecraft development team of the Fifth Academy of China Aerospace Science and Technology Corporation for several years.
In order to adapt to the different configurations of the space station assembly and the different docking states of the visiting spacecraft, and to realize the forward, backward, and radial rendezvous and separation with the space station, the development team designed new rendezvous paths and orbiting modes, and increased the orbiting, Fast rendezvous and docking, radial rendezvous and docking functions.
The complex scene of radial rendezvous and docking also puts forward higher requirements for microwave radar.
"Microwave radar is a medium and long distance measurement method. During the rendezvous and docking process, when the spacecraft is about 90 kilometers away from the core module, the microwave radar starts to work, providing accurate ranging and speed measurement information between the two spacecraft, and achieving long-distance capture. , Stable tracking and precise measurement.” According to Yao Yuanfu, chief designer of microwave radar at the 25th Institute of China Aerospace Science and Industry Corporation, the second-generation microwave radar is installed on Shenzhou 13 with small size, light weight and power consumption. Low, in addition to the basic high-precision measurement function, it also has a communication function, which can communicate with different transponders according to switching instructions, and realizes the docking of multiple pairs of interfaces in the core cabin.
How precise is the measurement accuracy of microwave radar?
The developers made an interesting analogy: similar to the A4 paper that was identified in Shijiazhuang from Beijing.
How is high-precision measurement achieved?
"Microwave radar uses the principles of pseudo-code ranging, Doppler velocity measurement, and interferometer angle measurement to achieve high-precision measurement of the relative distance, velocity, and angle between the two devices." Yao Yuanfu said.
It is understood that both radial rendezvous and forward rendezvous are the normal rendezvous methods for the manned spacecraft of the Chinese space station, and will be used alternately in future manned rendezvous and docking missions of the space station.
3 The USB measurement and control network covers land, sea, and space bases, and the aerospace measurement and control communication performance is stronger
"Optical tracking is normal", "USB radar tracking is normal", and "telemetry signals are normal"... the rocket took off from the Jiuquan Satellite Launch Center. After tens of seconds, the various "normal" passwords issued by the staff in the command hall echoed in the launch site. Night sky.
The USB measurement and control network (unified S-band measurement and control network) is indispensable for hearing the reassuring "normal". It includes numerous measurement and control stations and the "Yuanwang" measurement and control ship deployed on the ocean, which can measure and control rockets and rockets in real time. The flight status of the spacecraft.
In the manned space mission, the Xi’an Satellite Measurement and Control Center serves as the orbital calculation backup center, and the Beijing Aerospace Flight Control Center is jointly responsible for the precise tracking, monitoring and calculation and analysis of the spacecraft during launch into orbit, on-orbit operation, and return and reentry phases.
"Since the launch of the manned space project, after nearly 30 years of exploration and practice, China has built a USB measurement and control network covering land, sea, and space." The system is compatible with the world and integrates the functions of orbit measurement, telemetry, remote control, voice, and television. It integrates the functions of measurement and control and space-to-earth communication. It is the only information line for the spacecraft to contact the ground after it is launched.
The entire process of the radial rendezvous and docking is completed by the spacecraft intelligently and autonomously under the command of the guidance, navigation and control (GNC) system.
"In the process of rapid autonomous rendezvous and docking, the ground basically does not need intervention and control, mainly relying on the sky-link relay satellite for tracking, measurement and control." Zhang Zhuo said that the overall performance of land-based USB measurement and control equipment is relatively more stable, and various situations in space are unknown. In the case of circumstance, by complementing each other with relay satellites, forming a world-earth integrated measurement and control network to jointly escort the astronauts’ space journey.
According to Xie Jianfeng, the chief engineer of the Shenzhou 13 mission of the Beijing Aerospace Flight Control Center, the mission team has overcome many technical difficulties in the face of new docking methods, long on-orbit time, and high handling requirements.
During the radial rendezvous and docking, the space station assembly and the spacecraft have a large attitude adjustment, which affects the relay measurement and control and spacecraft energy, and brings changes to the measurement and control support mode and flight procedure arrangement. This increases the difficulty of ground monitoring and emergency response.
The task team optimized the design plan, refined the decision-making criteria, and innovatively designed the measurement and control mode based on air-to-air transmission and the grid-connected power supply mode, which overcomes the communication and power supply problems, and greatly improves the safety of rendezvous and docking.
"In order to ensure timely and effective handling of emergency failures, we have designed more than 400 failure plans for the Shenzhou 13 mission, with as many as 2500 combined plans. In the most urgent case, the order must be handled within 15 seconds." Sun Jun said.
The SAW filter is a device used to filter out high-order harmonics, image information, transmit leaky signals, and various parasitic clutters and other interference signals to ensure that the spacecraft's communications are clearly transmitted back to the ground.
The SAW filter developed by the 23 Microelectronics Company of the Second Academy of China Aerospace Science and Industry Corporation provides communication guarantee services for key parts of the Shenzhou 13 spacecraft.
The use environment is different, the environmental requirements that the sound meter device withstands are very different.
For example, in the rocket launch stage, the device is subjected to huge acceleration, and the SAW filter needs to work normally under severe vibration and shock; in the orbital flight stage, the device works in a weightless environment, and the pressure inside and outside the shell varies greatly. It can maintain normal shape and function under strong radiation and high pressure.
Taking these special needs into consideration, during the development of the device, the developers have done product stress design, reliability design and radiation protection design according to different use environments to ensure that the device works normally under extreme environments and the communication is clear and reliable.
Our reporter Chai Yaxin reports from Dongfeng Aerospace City