New technologies in chemical materials for Shenzhou-13

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To ensure an appropriate temperature inside the cabin, the main method for controlling the temperature on the spacecraft is to use thermal protection structures to shield the cabin. The technical staff designed a heat-resistant coating on the surface of the capsule, applying a layer of ablation heat-resistant material. This heat-resistant material undergoes a series of endothermic reactions such as decomposition, oxidation, and sublimation under high-temperature conditions, thereby removing a large amount of heat and protecting the internal structure. In \"A Day in Space,\" which is included in middle school Chinese textbooks, Yang Liwei mentioned: \"The rapidly moving spacecraft experiences friction with the atmosphere, and the resulting heat turns the area outside the windows red; then, outside those red-colored windows, red and white fragments keep passing by.\" The outer surface of the spacecraft is equipped with an ablation shield that is resistant to high temperatures; as the temperature rises, this shield begins to peel off, and in doing so it absorbs some of the heat. ” 　　This material features a honeycomb structure, which provides the highest strength at the same density; it stands out among the more than 100 heat-resistant materials developed to date, being capable of withstanding temperatures as high as 2000°C and thus ensuring the safe return of the Shenzhou spacecraft. Furthermore, to prevent this material from expanding and contracting due to temperature changes, thermal insulation materials cannot be tightly bonded to the load-bearing structural materials without any treatment; the stress generated can be sufficient to cause cracks in the thermal insulation layer, leading to unimaginable consequences upon return. The American Apollo spacecraft had sliding trusses added between the heat shield and the structural layer. The Shenzhou spacecraft adheres the heat shield directly to the structural shell, resulting in a simpler design and lower weight. 　　In addition, key components of the Shenzhou-13 manned spacecraft also incorporate integrated heat-resistant/insulating medium-density premixes developed by China National Building Materials Group Co., Ltd., high-strength yarns, as well as phenolic hollow microspheres produced by Jinan Shengquan Group Co., Ltd. The integrated heat prevention/insulation medium-density premix can effectively provide heat prevention and insulation functions, maintaining an appropriate temperature inside the return capsule; high-strength yarns can be used in the insulation layer of the return capsule to meet its requirements for temperature resistance, heat retention, and durability. Phenolic hollow microspheres are new materials with a special hollow structure, featuring an air or other gas core surrounded by a phenolic resin layer. They have characteristics such as small particle size and low density, and can provide functions like ablation resistance, thermal insulation, and electromagnetic wave absorption, thereby keeping the temperature inside the return capsule within safe limits and ensuring the proper operation of the components in the capsule as well as the safety of the astronauts. 　　The Shanghai Institute of Ceramics, Chinese Academy of Sciences, also made significant contributions to the successful completion of the Shenzhou-13 manned space mission. Various coating materials developed by the institute have been put into use, including long-life, low-expansion ratio inorganic thermal control coatings, high-temperature resistant insulation materials and components, ablation-resistant coatings for the reentry capsule’s portholes, thermal protection materials for attitude control engines, porthole glass and optical coatings, heat-shielding antenna windows for the reentry capsule, and stray light reduction coatings. Among them, the anti-ablation contamination coating on the return capsule’s windows retained its excellent self-cleaning properties even after 183 days of extravehicular operations in orbit. This ensured that the windows remained transparent despite being contaminated by volatiles from ablation materials during the capsule’s re-entry into the atmosphere, allowing astronauts to observe the outside environment effectively through the windows throughout their return to Earth. It also enabled ground rescue teams to assess the condition inside the capsule right after the spacecraft landed by looking through the windows. 　　In addition to maintaining the proper temperature, the return capsule also requires its speed to be controlled precisely. The Shenzhou spacecraft travels in orbit at a speed close to the first cosmic velocity. At such high speeds, it is necessary to control the final landing speed upon returning to Earth in order to ensure the safety of the astronauts. To achieve this goal, technical personnel conduct numerous tests and data analyses during the spacecraft development phase to ensure that the spacecraft gradually reduces its speed during landing. Before returning, the thrusters in the reentry capsule are used to apply braking, reducing the orbital energy and altitude so as to ensure the spacecraft’s re-entry into the atmosphere. The reentry capsule has a specific aerodynamic shape; once it enters the atmosphere, it slows down due to the drag and lift generated by aerodynamics. When the capsule is near the ground, a parachute is deployed to further reduce its speed. At the moment of landing, the landing thrust engines located at the bottom of the reentry capsule are activated, ultimately bringing the landing speed within a certain range. In addition, to reduce the landing impact on astronauts, Southeast University developed aluminum foam energy-absorbing components for the return capsule of the Shenzhou-13 spacecraft. The research team tasked with this development work has extensive experience in areas such as the production of aluminum foam and the study of its properties; it has developed a variety of porous material components for various spacecraft, including those used in the Shenzhou series up to Shenzhou 5, as well as for satellites like Fengyun-4.