Spacewalk: Experiencing a "dangerous romance"

As we all know, up to now, my country has carried out two extravehicular activities during the space station phase and achieved complete success. Extravehicular activities, together with manned round trips between the earth and the sky and rendezvous and docking, are known as one of the three basic technologies of manned space flight. They play a unique and important role in the development of manned space flight, especially in the construction of space stations, space maintenance and repair, and space rescue. Let us take a closer look at this dangerous and romantic mission.

my country's first astronaut spacewalk during space station phase

· Four levels of space environment

Extravehicular activities are also called spacewalks. Extravehicular activities are a general term for a series of processes in which astronauts leave manned spacecraft or bases built on other celestial bodies, rely on their own life support systems, work and move in space or on the surface of other celestial bodies, and then return to the manned spacecraft or base. Manned spacecraft here include spacecraft, space shuttles, space stations and lunar modules.

Spacewalk is one of the most dangerous tasks in space activities. Astronauts leave the protection of the spacecraft and go into the vast space alone, floating in orbit at a speed of nearly 8 kilometers per second, facing the test of the harsh space environment such as vacuum, strong radiation, weightlessness and sudden cold and hot alternation.

First, in a vacuum environment, if astronauts lose effective protection, they will lose consciousness due to lack of oxygen within 15 seconds and die within 30 seconds. Due to the lack of atmospheric pressure, the blood and body fluids of the human body will "boil" like boiling water, and the skin, tissues and organs will also expand outwards.

Secondly, there is no barrier of the Earth's atmosphere and magnetic field in space, and astronauts will be directly exposed to various cosmic radiations, including solar rays ejected during solar flares, high-energy particles from the Milky Way, and non-ionizing radiations such as ultraviolet rays, infrared rays, and radio frequency radiation. These radiations can cause varying degrees of harm to the human body. If they exceed the safety limit, astronauts will suffer from radiation sickness or even be life-threatening.

Thirdly, in the weightless environment of space, astronauts will suffer from vestibular dysfunction, resulting in dizziness, nausea, vomiting and other "space motion sickness". Long-term weightlessness will increase the excretion of inorganic salts such as calcium, phosphorus and magnesium in the human body, causing osteoporosis and muscle atrophy.

In addition, there is no air in space, convection disappears, and the temperature changes very drastically. The space station orbits the earth in 90 minutes, half of the time it is exposed to the sun and half of the time it is blocked by the earth. When it is exposed to the sun, the temperature exceeds 100 degrees Celsius, and when it is blocked, it drops to minus 100 degrees Celsius. In this extreme environment of sudden cold and heat, astronauts' continuous spacewalks for several hours are a great test of their physical and mental health.

Astronauts need to face these four levels of the space environment when walking in space, and the extravehicular spacesuit is the ultimate guarantee to meet the tests.

Chinese extravehicular space suit

The extravehicular space suit consists of clothing, helmet, gloves and space boots, among which the most complicated is the clothing, which has 6 layers from inside to outside. The innermost layer is the lining and urine collection device; the second is the liquid cooling ventilation layer for heat dissipation; the third and fourth layers are respectively the pressurized airtight layer to maintain the pressure inside the space suit and the restricting layer to limit the outward expansion of the pressurized airtight layer; the fifth layer is the thermal insulation layer to cope with the extreme temperature difference outside the cabin; the outermost layer is the protective layer, which is made of a variety of fiber composite fabrics, has good softness, and is resistant to penetration, wear, high temperature, combustion, corrosion, and radiation, and has other equipment interfaces.

In addition, the extravehicular space suit also provides an independent backpack-type life support system, a gas-liquid-electric support system, and measurement, control, and communication devices. It can be said to be a most miniature spacecraft.

· Spacewalk preparation· Before a spacewalk, the astronauts' preparations for going out of the cabin are also very complicated. They need to operate hundreds of devices, which places high demands on professional knowledge and operating skills. Astronauts must be clear about the shape, location, operation method, operating essentials and related actions of any device. They need to prepare for many days before going out of the cabin, and they need to prepare for several hours in advance on the day of going out of the cabin.

Chinese astronauts inspecting their space suits outside the spacecraft

The astronauts first put on their extravehicular suits, conduct system checks on the extravehicular suits and the docking system of the extravehicular suits, and then "drill" into the suits to adjust the size, check the airtightness, and conduct full performance tests to ensure that everything is normal. During the "dressing" process, the two astronauts cooperate with each other, one operates while the other reads the operation manual to confirm, to ensure that all steps are foolproof.

The second step is to conduct on-orbit training. After putting on the extravehicular suit, astronauts need to move and perform various simulated operations to experience the characteristics of moving and operating in a weightless state. Although there are neutral buoyancy tanks on the ground to provide weightless training, there is still a big gap compared to the real space environment.

At the same time, the astronauts need to find the right position to open the hatch and the points for their hands and feet. During the on-orbit training, the astronauts need to rehearse the entire on-orbit preparation and extravehicular activities to further familiarize themselves with the extravehicular procedures, but the amount of exercise should not be too much to prevent space motion sickness. After these tasks are completed, the astronauts will rest for a period of time.

The last step is the airlock procedure and door opening. Astronauts enter and exit the space station through the airlock. After entering the airlock, the inner door is closed, the extravehicular suit is pressurized, and oxygen is inhaled and nitrogen is expelled to avoid decompression sickness.

Preparation before leaving the cabin

The airlock cabin slowly depressurizes, and when it drops to 3 kPa, the air-liquid combined connector of the extravehicular suit is disconnected from the spacecraft, and the suit switches to fully autonomous oxygen supply and cooling.

When the air pressure drops to about 1 kPa, the outer door can be opened. When opening the door, unlock it first, wait until the pressure inside and outside the cabin is balanced, and then open the door completely. Before leaving the cabin, the astronauts also need to cover the door with a protective cover to avoid scratches when entering and leaving the cabin. During this process, the astronauts always use one hand to stabilize their bodies and complete all actions with only one hand.

After several hours of preparation, astronauts can officially carry out extravehicular activities.

· Coordination between heaven and earth for spacewalk· When astronauts go out of the cabin for spacewalk, they are governed by the laws of physics. It is an extremely dangerous job. If they are not careful, they will be catapulted into space by the space station. They need to follow a complete set of actions and technical specifications.

According to calculations by experts at home and abroad and the experience of the International Space Station, after leaving the spacecraft, astronauts will maintain several different relative motion trajectories with the space station (related to the point of leaving the spacecraft), and the astronauts' motion orbit is usually elliptical. The force and angle used by astronauts when leaving the spacecraft will affect their orbit during "space flight". If the force and angle are slightly deviated, they will fall into space, so astronauts must have a wealth of physics knowledge and undergo thousands of trainings before they can conduct spacewalks.

Chinese astronauts are conducting extravehicular operations

During extravehicular activities, astronauts must fasten safety ropes. To facilitate the movement of astronauts, handrails are specially installed outside the space station so that astronauts can move their bodies like rock climbing, which requires good arm and physical strength. During the first spacewalk during the Chinese space station phase, one astronaut used the traditional method of moving with the handrails outside the space station, while the other used a robotic arm to assist in the movement. At the same time, the various subsystems of the ground measurement and control center worked closely together to establish communication connections through the Tianlian series of satellites, providing high-speed voice and image relay services for the ground to observe the astronauts' extravehicular status in real time and for the dialogue and communication between astronauts and the ground.

With the coordination between the ground and the space, and close cooperation inside and outside the cabin, the two astronauts completed the installation of foot limiters and extravehicular workbenches on the robotic arm, cooperated with each other to carry out operations such as assembling relevant equipment outside the space station, and jointly completed the lifting operation of the panoramic camera outside the space station.

During the second extravehicular activity during the space station phase, the two astronauts completed tasks such as the installation of the extravehicular expansion pump group and the lifting of the panoramic camera D. The whole process was smooth and successful, which further tested the functional performance of my country's new generation of extravehicular space suits, the ability of astronauts to work together with the robotic arm, and the reliability and safety of related support equipment for extravehicular activities.

my country's astronauts' second spacewalk during space station phase

In order to ensure the safety of astronauts' spacewalks, the best time for extravehicular activities must be chosen, which is the extravehicular window.

The time selection should take into account the safety of people and equipment, and should be arranged in the sunlit area as much as possible. When the space station is in low-Earth orbit, it crosses the South Atlantic Anomaly many times. The abnormal radiation in this area has an impact on electronic equipment and instruments, and is also very harmful to the human body. Therefore, extravehicular activities must be arranged to avoid this area.

(China Aerospace News)