What do astronauts do when they go out for a walk?

The recent "Feel Good" team

Going out for a walk is all over the screen again!

This is the first extravehicular activity after the full completion of the Chinese space station.

But the team's "walk" is not just about going out for a walk

While they are "taking a walk", they also have to do these...

On February 10, astronauts Fei Junlong and Zhang Lu, with the close cooperation of astronaut Deng Qingming in the cabin, ended a seven-hour extravehicular activity and successfully returned to the Wentian laboratory module.

Screenshot of the Shenzhou 15 extravehicular activity

Some of you may be curious: we often see news about astronauts going out of the spacecraft in the media. What do they do when they go out? In fact, as one of the core technologies in the field of manned space flight, there are many types of extravehicular activities, which can be roughly divided into the following three categories.

Category 1: Verification of extravehicular technology

A successful EVA requires a lot of supporting technologies, from the space parts such as spacecraft, astronauts, and space suits to the ground parts such as measurement and control communications, flight control, and mission management. Moreover, EVA applies the "bottom of the barrel theory": as long as there is a leak, all the water will flow out, resulting in a complete failure. For this reason, in the nearly 70 years since the beginning of the human space age, only the Soviet Union/Russia, the United States, and China have independently mastered this complex technology category.

Chinese astronauts' water tank training scene (Source: Our Space)

This technological development process is also the result of continuous iterations of "theoretical demonstration-simulation experiment-technical verification". For example, in addition to theory and simulation, major astronaut centers around the world have huge water tanks with various spacecraft models placed inside. After astronauts put on their space suits, they control the balance between buoyancy and gravity to simulate the effect of weightlessness in space, and repeatedly practice extravehicular activities to expose problems as much as possible. However, water tank exercises are also very limited. It is impossible to simulate the vacuum, weightlessness, and strong radiation scenes in space. It is necessary to go to space for a comprehensive test with real weapons. Every new technology proposed is iterative in this way.

In the early days of extravehicular activities, the space suit had to be connected to the manned spacecraft through an "umbilical cord" to obtain supplies. Later, portable space suits began to be widely used. After the astronauts wore portable space suits, they turned into a small independent spacecraft. The emergence of manned maneuvering devices is even more eye-catching in a "science fiction" way. Astronauts can fly freely near the spacecraft by controlling small engines while sitting in the device.

Manned Maneuvering Unit (Image source: NASA)

Each of the above technological iterations needs to be verified. For example, as early as 2008, during the Shenzhou 7 mission, astronauts Zhai Zhigang and Liu Boming verified the feasibility of extravehicular activities, which also meant that my country's manned spaceflight has entered the era of extravehicular activities, and has been iteratively developing ever since.

Not only the overall plan needs to be verified, but also the specific technologies need to be tested. The essential guarantee for astronauts to go out of the cabin is the extravehicular space suit, which can be directly regarded as a miniature spacecraft. my country's "Feitian" extravehicular space suit has gone through years of accumulation, but its application also needs to be tested in space; the only way to go out of the cabin is the airlock cabin responsible for the transition between the cabin and the outside (vacuum). Every manned spacecraft (Shenzhou spacecraft, Tiangong 1/2 spacecraft, Tianhe core module, Wentian experimental module) needs to be equipped with (or use both), and its on-orbit performance is related to the success or failure of the entire mission; extravehicular activities require frequent use of robotic arms for assistance, and its space performance capabilities need to be tested; during the activities, the coordination between the cabin and the outside, the ground-to-ground communication measurement and control guarantee, the ground process control, the emergency evacuation, etc., these scenes cannot be simulated on the ground, and must be tested through real extravehicular activities.

Just as real military exercises can expose problems and summarize experience, a considerable number of extravehicular activities are aimed at verifying the relevant technical systems.

Zhai Zhigang’s classic line, “I have left the cabin and feel good,” is exactly the desired effect of this type of extravehicular activity.

Category 2: Manned spacecraft installation and maintenance

The design and manufacture of manned spacecraft is much more difficult than that of unmanned spacecraft, especially for large space station module-level spacecraft. For example, the core module "Tianhe" and the two experimental modules "Wentian" and "Mengtian" of the Tiangong space station are too large. They are about 18 meters long and 4.2 meters in diameter, setting a record for the size of a single module in human spaceflight. But this is not the whole picture: this size is close to the limit allowed by the fairing of the "shorty and fat man" Long March 5B. Other panoramic cameras, extravehicular expansion pumps and external instruments cannot be fully installed and deployed before launch, and must be assembled after entering space.

Friends may wish to recall that the extravehicular activities repeatedly mentioned in previous news mostly have keywords such as "lifting the panoramic camera" and "installing the extravehicular expansion pump set", and generally occur after the important compartments are launched and assembled. This is the first extravehicular activity after the completion of the Chinese space station, and an important task is also to install the extravehicular expansion pump set. It is the power heart of the thermal control circulation system inside and outside the spacecraft. Together with the heart inside the cabin, it can ensure the normal operation of the entire compartment. The panoramic camera is used to monitor the overall external condition of the spacecraft. There are also some external instruments and equipment. Only when all the external parts are complete can the spacecraft be considered to have met the design requirements.

Artistic rendering of the overall view of China's space station

In addition, it is impossible for any spacecraft to be completely free of problems, especially for large modular multi-module manned spacecraft at the space station level, especially it needs to fly stably for a long time. For example, the International Space Station has achieved about 500 tons and has been flying for 25 years, and the Chinese space station has nearly 100 tons and has a flight time of at least 10 years. During this period, if various problems may occur in the space station, they must be repaired in time, especially when there are problems outside, which can almost only be repaired by astronauts' extravehicular activities.

To explain this extravehicular activity in plain language, it is: once the rough house (cabin section) is built, the decorators (astronauts) start decorating it to make the house (space station) more livable. If there is a problem, the decorators will come and fix it so that the house can be lived in comfortably.

Category 3: Scientific research and application

The fundamental goal of manned space flight is to use the unique space of space to expand the scientific boundaries of mankind. After the space station is built, it will become a long-term manned space laboratory, allowing astronauts to carry out various scientific research. This is the core motivation for aerospace powers to invest heavily in manned space flight.

The International Space Station and the Chinese Space Station are equipped with various experimental cabinets to carry out various experiments that netizens "cannot understand". However, some research must be carried out outside the cabin, such as scientific research related to astronomical observations, vacuum exposure, and extravehicular radiation. Some scientific instruments and equipment cannot be fully operated by the robotic arm system, so they must rely on astronauts' extravehicular activities to install, recover, and replace them, which becomes the key to the success or failure of scientific research. Since the recruitment of the third batch of astronauts, my country has begun to cultivate "load expert" roles, and their main business will be focused on scientific research.

The Tianhe core module and the Tianzhou-2 cargo spacecraft

Various types of manned spacecraft are also "space motherships". Miniature spacecraft (astronauts) depart from here and can also serve goals other than manned spacecraft. For example, in the era of the space shuttle, there have been many scenes of recovering failed satellites and returning to Earth. The famous Hubble Space Telescope encountered a series of technical problems after its launch, which made it impossible to work normally. Later, it was completely repaired through 5 consecutive extravehicular activities, and almost all major scientific instruments were replaced, so that this legendary telescope was reborn and has been working until now, reshaping human astronomy. The large-scale survey telescope that my country is about to launch will enter a flight state with the space station in the future. One of the main reasons is that in the future, astronauts can repair and update it through extravehicular activities to ensure its long-term working condition.

In addition, manned landing on the moon, including the expected manned landing on Mars in the future, can also be regarded as a very complex extravehicular activity. my country's white paper "China's Spaceflight in 2021" has clearly defined important goals such as the full construction and operation of the Chinese space station, the implementation of the fourth phase of the lunar exploration project, and the deepening of the demonstration of the manned lunar landing program. In the foreseeable future, Chinese astronauts will set foot on the moon and complete an extravehicular activity from myth (Chang'e flying to the moon) to reality.