Plastic space window : Protect the astronauts like "eyes"

Introduction to the Space Window Project Team
National "973" Program "Polymer Molding Simulation and Research on Key Problems in Design and Manufacturing ”The project is jointly undertaken by Academician Shen Changyu, as the chief scientist, and 11 units in China With the background of design and manufacturing, it is committed to solving the problems of "Forming", "Maturity", "Serviceability" and "Process Control and optimization ”And other key issues to provide theoretical and technical support for China's transformation from a manufacturing power to a manufacturing power.
At 7:30 a.m. on October 17, the Long March 2F carrier rocket carrying the Shenzhou XI manned spacecraft ignited and launched at Jiuquan Satellite Launch Center. About 575 seconds later, the Shenzhou XI manned spacecraft successfully separated from the rocket, entered the predetermined orbit, and successfully sent Jing Haipeng and Chen Dong into space. The flight crew was in good condition, and the launch was a complete success.

China's self-developed spacesuit
Two days later, the manned spacecraft carrying two astronauts successfully docked with Tiangong-2, and began to carry out a number of space science experiments and space applications, especially the rendezvous and docking technology of the operating orbit of the space station. After the astronauts enter the Tiangong-2 space laboratory, they will carry out a mid-term stay test to assess the ability of the combination to ensure the life, work and health of astronauts, as well as the ability of astronauts to carry out flight missions, which will take a solid step forward for the construction of the third step space station of China's manned space engineering strategy.
In order to explore the mysteries of the universe, astronauts must wear spacesuits made of special materials, special processes and special technologies for space flight and even extravehicular activities. On the spacesuit, the space window on the helmet is one of the important parts, which not only directly affects the astronauts' observation of outer space, but also always affects the astronauts' life safety!
Extremely harsh conditions for manufacturing aerospace window
On September 27, 2008, astronaut Zhai Zhigang, wearing the "Feitian" spacesuit developed by China, left a figure of a Chinese astronaut in space, which also made China the third country to master the technology of space extravehicular flight. When Zhai Zhigang saw the space through the space window on his helmet and stretched out his arms to the space, as the developer of the space window, we felt extremely proud!
The spacesuit is generally composed of pressure chamber, helmet, gloves and boots, which can be divided into two categories: internal and external spacesuits. The helmet face window assembly is a window for astronauts to observe the outside world when they are in outer space activities. It can be said to be the "eye" of astronauts. It not only provides astronauts with a clear and good vision, but also is one of the most critical components for the life support of astronauts.
Of course, the space window is different from the window on the helmet that we usually wear when riding a motorcycle, because there are too harsh temperature difference conditions in space, as well as countless unpredictable dangers, which put forward extremely stringent requirements for the materials and design of the space window.
First, the space window should be able to withstand the extreme temperature environment in space. Since there is no air heat transfer and dissipation in space, the side of the space window directly exposed to the sun can produce a high temperature of up to 100 ℃. On the other side of the shade, the temperature can be as low as - 100 ℃. Therefore, the first thing for the space window is to be able to withstand extreme thermal expansion and contraction.
Secondly, the aerospace window must be free of defects. Since there is zero atmospheric pressure in space, any defect will expose astronauts to space, and they will face four major risks of pressure loss, hypoxia, low temperature and radiation damage. If people are directly exposed to space, hypoxia will quickly suffocate them to death. At the same time, without atmospheric pressure, people will die immediately due to the bursting of internal organs and organs. In addition, in the super low temperature environment of minus 269 ℃ in space, people will freeze to death immediately.
The experiment shows that if the spacesuit decompresses quickly, the astronaut will die in 15 seconds - this is the time when the body uses all the oxygen in the body.
Secondly, space windows should be able to block space radiation. Without the protection of the earth's magnetic field and atmosphere, astronauts will suffer more intense radiation damage from outer space.
Finally, there are countless pieces of space debris in space. As astronauts may encounter the impact of space debris with enough high kinetic energy from space at any time when they are outside the spacecraft or space station, the space window must be able to withstand the impact of these unprepared high kinetic energy space debris when encountering these debris.
Making space windows is not a simple technical job
Since the conditions for manufacturing aerospace windows are so strict, what materials are transparent aerospace windows made of?
In fact, we are not unfamiliar with it, it is a kind of , a kind of resin that is the same as our glasses and car lamp shades —— or A copolymer mixture of.
     It is a kind of linear carbonate polyester. The carbonate group in the molecule is alternately arranged with other groups. It belongs to the polymer containing carbonate group in the molecular chain. Polycarbonate is an almost colorless amorphous polymer in the glassy state, but its strength and optical properties are unparalleled.
However, due to the high molecular weight, rigid molecular chain, high viscosity and poor flow performance of polycarbonate, it is necessary to use polycarbonate to cause poor molding performance, high internal stress of products, large impact of environmental stress, and easy deformation and cracking, all of which bring great difficulties to the molding and processing of aerospace windows on helmets.
"Although polycarbonate has such a bad temper, we still have to shape the space window. After a variety of experimental studies, we decided to adopt the most common Forming method ——Injection molding.
Non Newtonian The melt is driven by the pressure to fill the mold cavity with lower temperature through the runner and gate. In this process, on the one hand, the melt is cooled rapidly due to heat transfer of the mold, and on the other hand, heat is generated due to high-speed shear. At the same time, it is accompanied by complex physical changes such as melt curing, volume shrinkage, orientation and possible crystallization, and even accompanied by chemical changes of macromolecules and from small molecules to large molecules.
With this process, The products have excellent physical and mechanical properties and superior service performance under specific working environment. This property comes from the composition of materials and different levels of structures, including micro and nano structures. The formation and evolution of different levels of structures depend on mold design, manufacturing and process conditions. It can be said that the forming process not only makes the material obtain a certain shape and size, but also gives the final structure and performance of the material.
Focusing on this topic, since 2007, the scientific research team of the National Rubber and Plastic Mold Engineering Research Center of Zhengzhou University has started the research and development work of the space mask window of the spacesuit helmet.
Without any experience for reference, our team combined the use environment and function of the face window, finally used optical grade polycarbonate as the resin, combined with numerical simulation technology, designed and processed precision molds, developed the face window of the space suit helmet by injection molding method, and applied nano gold coating to the outermost face window to block the ultraviolet rays in space.
At present, the space window has been successfully applied to the spaceship Shenzhou 7 astronauts' extravehicular suits and Shenzhou 9 astronauts' extravehicular suits. Our research team, as one of the 20 award-winning collectives in China, also won the award of "Outstanding Contribution to China's Manned Space Program".
Face the pressure and continue to serve the aerospace industry well
In 2008, after the successful launch of the "Refreshing Seven", Chinese people have always felt extremely proud. However, the United States N But in In 2010, a special report on China's space suits was put forward. The report specifically pointed out that China's extravehicular activities lasted only 18 minutes and did not experience long-term tests. This has become the starting point for the development of our new generation of space window.
In 2012, Zhengzhou University joined forces with University of Science and Technology of China, Shanghai Jiaotong University, Sichuan University, South China University of Technology, Huazhong University of Science and Technology, Northwest Polytechnical University, Institute of Mathematics and Systems Science, Chinese Academy of Sciences, Dalian University of Technology, Central South University The General Academy of Scientific Research, etc., has undertaken the national "973" plan project "Research on key problems in polymer molding simulation and mold design and manufacturing".
The project is based on the development of a new generation of aerospace window, focusing on the evolution law of different levels of morphological structure of polymer materials under complex multi field action, the cross scale calculation theory of polymer complex fluid in the process of molding, the cross scale analysis of polymer product performance and service behavior after molding The key scientific issues such as the theory and method of multi-objective optimization of molding process control and mold design are studied.
This project first needs to solve the life and aging problems of the aerospace window, and how to improve the aging performance by changing the macromolecular structure through various means such as material forming process product post-treatment. Secondly, the relationship between material, molding process, mold design and optical performance shall be solved to clarify the influence on transparency Molecular dynamics reasons for optical properties of components, molecular orientation and optical behavior (caused by optical distortion) caused by molding, etc., and finally, strength analysis of products in extreme environments.
After four years of research, the project team has made a series of achievements and successfully applied them to the development of the new generation of aerospace window in China.
In order to improve the anti-aging performance of the aerospace window, the project team studied the thermal stability of polycarbonate and proposed a random chain break/end chain break reaction kinetic model to describe the degradation kinetic process. At the same time, long-chain branched polycarbonates with different topological structures were prepared by high-energy gamma ray irradiation. With the introduction of long-chain branched structures, the chemical branching points and molecular chain entanglement formed in the process of long-chain branching effectively improved the environmental stress cracking resistance of polycarbonates.
To solve the problem of ultraviolet radiation aging of polycarbonate, we have established polycarbonate/nano titanium dioxide composite materials. Rutile nano titanium dioxide can absorb and scatter ultraviolet light. At the same time, in order to reduce the catalytic degradation of rutile on polycarbonate and maximize the UV aging resistance of polymer, Silicon dioxide is selected to coat nanometer titanium dioxide, which effectively improves the ultraviolet aging resistance of polycarbonate and shields ultraviolet light.
In order to control and regulate the optical performance of the aerospace window, the project team correlated the orientation degree of the molecular chain in the product with the optical distortion through the 2D-SAXS signal analysis of polycarbonate products, obtained the internal correlation between the injection conditions and the optical distortion of the product, and revealed the injection rate The relationship between the melt flow direction and the internal layers of the sample and the optical distortion of the product.
At the same time, the project team used the injection molding simulation theory to obtain the dynamic distribution of temperature field, pressure field and product stress field during the molding process, used the Lorentz Lorentz optical theory of the relationship between the refractive index of the medium and the molar polarization intensity to establish the relationship between the density field and the refractive index field of the product, and then used the Fresnel formula in the electromagnetic theory, The reflected light intensity and refracted light intensity are calculated, and finally the transmittance field of the product is calculated. These works lay a theoretical foundation for optimizing the molding process, regulating the internal structure of the product, and then controlling the optical properties of the product.
In order to realize the forming structure integration analysis of the aerospace window, the project team established a three-dimensional unified gas-liquid two-phase model and a level set method for tracking the moving interface. Using the smooth particle hydrodynamics method, the three-dimensional flow behavior of the aerospace window filling process was simulated under the Lagrangian framework. Through uniaxial tension and compression tests of polycarbonate at different strain rates and temperatures, a unified tensile compression constitutive model of polycarbonate was established. The constitutive model can effectively describe the complex mechanical properties of polycarbonate, such as the strain rate related effect, temperature related effect, softening, hardening, tensile and compression properties asymmetry, and lay an important foundation for reasonably predicting the service behavior of aerospace windows.
As the third step of China's manned space engineering strategy is approaching, we hope that the new generation of space windows made of engineering plastics will not only provide astronauts with the eyes to observe the space world, but also protect our astronauts' lives like eyes.