Shenzhou 18 was successfully launched! Uncover the technological secrets behind the Shenzhou spacecraft

At 20:59 on April 25, my country successfully launched the Shenzhou 18 manned spacecraft, sending three astronauts born in the 1980s, Ye Guangfu, Li Cong and Li Guangsu, to live and work in the "China" space station for six months.

This is the 18th launch of my country's Shenzhou series spacecraft. What is so special about my country's Shenzhou series spacecraft? Next, let us learn about the secrets of the Shenzhou spacecraft.

(At 20:59 on April 25, the Long March 2F Yao 18 carrier rocket carrying the Shenzhou 18 manned spacecraft was ignited and launched at the Jiuquan Satellite Launch Center. Image source: Xinhua News Agency)

1 Starting from a high point, the Shenzhou spacecraft came into being

my country's "Shenzhou" spacecraft is used for manned round-trip transportation between the earth and the sky. It began to be developed in 1992. At that time, considering that my country had a solid technical foundation and rich development experience in recoverable satellites, and could learn from the experience of foreign countries in developing manned spacecraft, it was finally decided to skip the 1-cabin and 2-cabin spacecraft, and start from the most advanced spacecraft at that time, and directly develop the 3-cabin manned spacecraft "Shenzhou", reaching the level of the international third-generation manned spacecraft. As of today, 18 "Shenzhou" series spacecraft have been launched, with a success rate of 100%, of which 13 are manned spacecraft, sending a total of 22 astronauts and 35 astronauts into space.

In addition, Shenzhou has other advantages, such as:

One ship can be used for multiple purposes. After the return capsule of several "Shenzhou" ships returned to the ground, its orbital module remained in orbit for another half a year, which is equivalent to launching a satellite for free.

High degree of intelligence. It adopts the latest achievements of information technology, from automatic control, guidance and navigation to data management, from redundant design to liquid crystal display equipment, its electronic technology and intelligence level are far ahead of Russia's "Soyuz" manned spacecraft. Its solar cell wings can automatically align with the sun.

Advanced heat protection technology. The maximum diameter of the Shenzhou spacecraft reentry capsule is 2.5 meters, the surface area is 22.4 square meters, and the total weight of the heat protection materials used is about 500 kilograms. The diameter of the Soyuz spacecraft reentry capsule is about 2.2 meters, the surface area is 17 square meters, but the total weight of its heat protection materials is 700 kilograms.

The parachute is very large. Its main parachute is 1,200 square meters. Its pilot parachute pulls out the drag parachute and straightens it; the drag parachute reduces the speed from 200 meters per second to 80 meters per second; the main parachute reduces the speed to 6 meters per second. The whole parachute is only as big as a small bag when folded up, and weighs only more than 90 kilograms.

2 Small but exquisite, the three major cabins of the Shenzhou spacecraft are revealed

Shenzhou consists of an orbital module, a return module and a propulsion module. It is nearly 9 meters long and weighs about 8.1 tons. It has a crew of 3 people and 6 cubic meters of free space for astronauts. When fully loaded with 3 people, it can carry at least 300 kilograms of cargo on the upper and 100 kilograms of cargo on the lower. It can fly autonomously for 7 days and dock for 180 days.

(Sketch of the Shenzhou spacecraft. Image source: China Manned Space Engineering Office)

The orbital module is located at the front of the spacecraft, and has an additional section or rendezvous and docking device for testing at its front end. When the spacecraft is flying alone, the orbital module is used for astronauts to work, eat, go to the bathroom and sleep after entering orbit, and is called the "first hall."

The return capsule is located in the middle of the spacecraft. It is the cabin for astronauts to travel back and forth, and is also the control center of the spacecraft, known as "Room 1". It has the ability to support astronauts to survive on land for 48 hours and at sea for 24 hours after landing.

The above two cabins are sealed pressure cabins for astronauts to move around, with a cabin pressure of 81.0-101.3 kPa; the temperature is 21℃±4℃, and the return process does not exceed 40℃; the noise is no more than 75 decibels in the operation phase, and no more than 125 decibels in the ascent phase and return phase. The flight axial overload is no more than 5g in the ascent phase and no more than 4g in the return phase.

The propulsion module is located at the rear of the spacecraft. It is a non-sealed structure that provides power, power, fuel, etc. The tail is equipped with four 2.5 kN orbit change engines, and the side walls are equipped with attitude control engines and a 24 square meter main solar cell wing with a power supply of 1.8 kilowatts.

3. Shenzhou spacecraft has 14 major subsystems , each with its own functions

"Shenzhou" consists of 14 subsystems. These subsystems involve dozens of disciplines such as physics and medicine, so they have technical diversity and development complexity. Among them, the environmental control and life support, recovery and landing, instrumentation and lighting, emergency rescue, crew and other subsystems are unique to manned spacecraft. In addition, the crew and payload subsystems belong to the onboard part of astronauts and space application systems. Some of the subsystems are as follows:

The structure and mechanism subsystem consists of the main body structure, heat protection structure and mechanism.

The environmental control and life support subsystem creates a suitable cabin environment for the spacecraft crew and provides them with water, oxygen, etc.

The thermal control subsystem is used to ensure the environmental temperature conditions required by the instruments, equipment, structures and crew in each cabin of the spacecraft.

The measurement, control and communication subsystem is used for tracking and measuring spacecraft orbits, transmitting spacecraft data and images, voice communications and television monitoring, etc.

The data management subsystem collects spacecraft engineering parameters and operating parameters at any time and processes the collected data.

The power subsystem is powered by solar cells and chemical batteries.

The emergency life-saving subsystem is responsible for the escape of the spacecraft while it is on standby on the launch pad and during the launch phase when a dangerous failure of the rocket or spacecraft occurs and cannot be eliminated.

The crew subsystem provides the spacecraft with qualified crew, space suits and space food to ensure the health of the crew.

4 Continuous optimization, the performance of Shenzhou spacecraft continues to upgrade

In order to meet the needs of the space station mission, my country has further improved the Shenzhou spacecraft starting from Shenzhou 12. For example:

Special designs have been made for the thermal control schemes of the return capsule, propulsion engines and tanks, as well as the ship-station grid-connected power supply scheme, so that the spacecraft has the adaptive supporting conditions for power supply and thermal environment protection to adapt to the complex external heat flow conditions brought about by the complex configuration and attitude of the space station.

The water storage equipment was changed from water tanks to water bags, saving space and weight; a heat circuit was added to the spacecraft cabin wall, changing from centralized control to branch control, achieving precise regional temperature control.

Due to the long time the spacecraft stays in orbit, the spacecraft uses a new type of low-absorption-low-emission thermal control coating, which is capable of resisting high-energy ultraviolet radiation, atomic oxygen bombardment, and attacks from various high-energy particles and ionizing radiation in space at all times.

The control computer and data management computer used in the spacecraft are completely powered by domestically produced CPU chips.

The Beidou navigation terminal is also introduced into the spacecraft design, and navigation calculations, return search and rescue landing point reports, etc. all use the Beidou system positioning data.

The measurement and control has shifted from mainly ground-based measurement and control to mainly space-based measurement and control, which not only expands the measurement and control coverage but also saves mission costs.

A rapid cabin door leak detector was used instead; products such as the international rescue position indicator and microwave gravity level switch were used to quickly and accurately find the return capsule; the cabin lighting equipment and rendezvous and docking lighting equipment used advanced solid-state lighting sources, which have the advantages of impact resistance, vibration resistance, low power consumption and high stability, adding an extra guarantee for the success of rendezvous and docking.

It is also worth mentioning that the Shenzhou 18 launched this time has new changes in the main power storage battery compared to previous Shenzhou spacecraft - from the previous cadmium nickel battery to lithium-ion battery. Lithium-ion batteries have higher energy density, longer cycle life, better high-rate charging, and reduce the weight of the entire ship by about 50 kilograms.

5. Efficient production and batch production mode enable high-quality delivery of Shenzhou spacecraft

After entering the space station era, in order to improve the quality of spacecraft, reduce development costs, and shorten the development cycle, "Shenzhou" adopts a batch production model. This can make the production and testing process more standardized and regularized, which is more conducive to personnel mastering product status and ensuring product quality. At the same time, it improves the concentration of material procurement and facilitates the control of the supply chain and the control of the stocking cycle.

The four manned spacecrafts from Shenzhou XII to Shenzhou XV form one group. After adopting this production model, the development process of the Shenzhou spacecraft before leaving the factory was reduced from 17 months to 14 months, and the launch site test and launch process was also optimized from 59 days to 46 days.

After the Chinese space station was fully built and entered normal operation, the "Shenzhou" series of manned spacecraft also ushered in a new batch (6 spacecraft, namely Shenzhou 16-21) of intensive production. Under the premise of ensuring reliability and safety, this batch of production completed hundreds of device changes and reliability improvement verification work in the shortest time and with the highest standards, further enhanced the autonomous health management function, and established a data envelopment analysis mechanism at the subsystem level, single machine level, and component level. It fully promoted the product data interconnection informationization, cable assembly layout digitization, and key parameter detection intelligence, fully realizing the re-upgrade of the "Shenzhou" spacecraft in the "space station era", laying a solid foundation for the "Shenzhou" to embark on a new journey.

The data display of the spacecraft instruments is simplified, providing a clearer, more intuitive and comfortable display interface for astronauts to perform their tasks. In addition, an upgraded relay terminal with three advantages of higher integration, stronger processing power and higher localization rate has been developed, which has achieved unimpeded communication between the spacecraft and the ground.

The research and development team continues to use information technology, automation, and intelligent means to further improve the efficiency of model development and ensure high-quality delivery of the cabin structure.

Author: Pang Zhihao, Chief Scientific Communication Expert of National Space Exploration Technology

Produced by: Science Popularization China x Chinese Society of Astronautics

Produced by: China Science and Technology Press Co., Ltd., China Science and Technology Publishing House (Beijing) Digital Media Co., Ltd.