On August 20, the three astronauts of Shenzhou XII once again performed the task of de-cabin, and Nie Haisheng and Liu Boming went out of the cabin, mainly installing the extravehicular thermal control expansion pump group, lifting the extravehicular panoramic camera, and assembling the extravehicular toolbox, and Tang Hongbo remained in the cabin to perform command and coordination tasks.
Push open the "door" of space, what kind of scenery is in front of you? If you want to walk in space, what kind of test do astronauts have to go through? Compared with Shenzhou 7 China's first spacewalk, what are the similarities and differences between the space station stage? In this regard, the reporter interviewed Yang Yuguang, vice chairman of the Space Transport Committee of the International Astronautical Federation and researcher of the Second Academy of China Aerospace Science and Industry Group.
Q: Why do astronauts carry out de-hatching activities? What can astronauts do outside the cabin?
Yang Yuguang: There are three basic technologies for manned spaceflight, namely the space-to-earth round-trip technology, the rendezvous and docking technology, and the extravehicular activity technology (also known as "spacewalk"). Since it is a basic technology, it shows that it is very important. Looking back at the development of manned spaceflight, extravehicular activities began in 1965, when former Soviet cosmonaut Alexei Leonov carried out the first extravehicular activities of mankind, when the development of this technology was mainly for the moon landing. Beginning in the late 1950s, the United States and the former Soviet Union engaged in a fierce space race with the goal of sending humans to the moon, and the technology of out-of-the-cabin activities had to be solved before astronauts could reach the lunar surface for activities.
After the realization of the manned lunar landing, the capsule technology has been successively applied in the construction of the space station and other space activities. In terms of space station construction, in the assembly and construction of the US "SkyLab I", the "Salyut" and "Mir" space stations of the former Soviet Union, and the international space station in operation, the astronauts' out-of-space activities have contributed to it, and even have the ability to turn the tide. For example, the United States "SkyLab I" after entering orbit seriously malfunction, thanks to the later launch of the Apollo spacecraft, three astronauts out of the cabin maintenance, so that it resumed normal work.
In addition to spacecraft maintenance and maintenance, the significance of the capsule is to carry out scientific research, including the collection of scientific research samples and the placement of scientific research equipment. In general, whether it is a manned lunar landing, a scientific expedition on the lunar surface, or equipment testing, maintenance and scientific research activities on the space station, the outgoing technology is indispensable.
Q: In order to successfully complete the mission, astronauts must be "all-rounders". What preparations do they have to do, and what skills do they master?
Yang Yuguang: In the early space activities, almost all astronauts were selected from the air force pilots, on the one hand, because of their good physical fitness, on the other hand, the operation of flying aircraft was extremely complicated, and they were very experienced in complex operations and emergency handling.
Extravehicular activities mainly place two main demands on astronauts. First, astronauts must have the scientific literacy of spacecraft maintenance and scientific experiments, knowledge reserves and operational capabilities; second, the extravehicular environment is special, weightless or microgravity conditions seriously restrict human mobility, if there is no adaptive training, it is difficult to operate in space.
From the perspective of space history, in 1965, after the former Soviet cosmonaut Leonov completed the first human spacewalk, american astronaut Edward White also performed a spacewalk, but the completion was not ideal and did not achieve the expected goal. By 1966, during the Gemini 12 mission, American astronaut Buzz Aldrin performed the last spacewalk of the U.S. Gemini program, which was very successful and lasted more than two hours.
Why was this spacewalk so successful? An important reason is that Aldrin is a lover of diving. As we all know, the floating state of a person in the water is very similar to the weightless state. The diving experience helped Aldrin complete the spacewalk with ease. Because of this, the "neutral buoyancy tank" has become the "standard" for astronaut training.
This environment is extremely physically demanding. After each tank training, the astronauts were sweating profusely, so tired from eating at noon that they couldn't even pick up chopsticks. But only after such training can they complete the task of "lifting heavy weights".
Q: We have seen that astronauts wear different spacesuits inside and outside the cabin. Is the extravehicular spacesuit also exquisite?
Yang Yuguang: Spacewalking is a high-risk behavior, and extravehicular spacesuits must provide all-round protection. It is the equivalent of a miniature, independent spacecraft. We see that when the Shenzhou XII astronauts were ready to leave the capsule, they did not put on our milky white extravehicular spacesuit at the beginning, but first put on a blue clothing with many tubes, which we called "ventilation liquid cold suit", which used water as coolant to cool the heat emitted by the body. Because the extravehicular spacesuit needs to shield the harsh conditions such as extravehicular space radiation and high and low temperature vacuum environment, it has strong sealing but poor heat dissipation. When people are active outside the cabin, the amount of activity is extremely large, and the heat generated by it must be taken away in time, and it is not enough to rely on ventilation alone, and it is also necessary to use a liquid with stronger thermal conductivity. This is only one aspect, the spacesuit is very complicated, and the astronauts also have to carry out relevant training, not simply "wearing clothes".
Q: The mission time of Shenzhou XII is obviously much longer than that of Shenzhou VII. How is the space station phase astronaut out of the capsule mission different from Shenzhou 7? Does this mean that the technology of extravehicular activities in our country has improved significantly?
Yang Yuguang: During Shenzhou 7, Chinese astronauts completed the spacewalk for the first time, which is equivalent to solving the problem of whether there is a problem. Taking the airlock chamber as an example, the astronaut moves from the normal atmospheric pressure environment in the cabin to the vacuum environment outside the cabin, and needs to transition through the airlock chamber, and the airlock chamber can gradually depressurize to the vacuum state before opening the hatch to exit the cabin. The Shenzhou VII spacecraft consists of three modules: an orbital module, a return module, and a propulsion module, and it uses the orbital module as an airlock module. The internal volume of the Shenzhou spacecraft return module plus the orbital module is only about 7 cubic meters, and later I also heard Liu Boming make a report, they carried out various operations, and the hands could only move along the gap in the spacesuit, which showed how small the space was.
They also had problems at the time, such as difficulty opening the hatch when leaving the cabin, and sensor failures that led to false fire alarms. The complexity and high risk of space activities can be seen from this, so it is said that under quite limited conditions, Zhai Zhigang successfully went out of the capsule to wave the five-star red flag and retrieved a sample outside the capsule back into the cabin, which is undoubtedly an important milestone in China's aerospace.
In contrast, Shenzhou XII's airlock module (the node cabin of the Tianhe core cabin) is more spacious, the exit hatch is opened more smoothly, and it also shoulders more key technical verification work. For example, robotic arm operation, emergency return, scientific instrument installation, etc., the operation is much more complicated than before. It should be said that from the perspective of the significance of the entire flight mission, the Shenzhou XII mission is of greater significance for the verification and mastery of key technologies, and also lays a good foundation for the subsequent construction of space stations and scientific experiment activities.
Q: You also mentioned the robotic arm, which is called the space intelligent mechanical system with the highest complexity, the largest scale and the highest control accuracy among similar aerospace products. What role can it play and what role does it play in extravehicular activities? Does the INTERNATIONAL SPACE STATION also have a robotic arm, and is it an essential tool for the space station?
Yang Yuguang: The robotic arm was originally manufactured in Canada, also known as the "Canadian arm" at the time, and was first developed in the United States space shuttle. In the early 1980s, after the first flight of the US space shuttle, it quickly used the robotic arm to release satellites, capture failed satellites and other space operations; the maintenance of the Us Hubble space telescope, the construction, maintenance, and scientific research of the International Space Station also played an important role. It can be said that as long as high-complexity space activities such as the space station are carried out, the robotic arm is a "must-have".
The Tianhe core module is equipped with a robotic arm, which can carry up to 25 tons of weight, and is the "Hercules" in the space station mission, which we call the "big arm". In the future, there will be "small arms" on the Q&M and Dream Experiment modules. The big arm is about 10 meters long, the forearm is 5 meters long, and the two robotic arms are operated like two hands, and the combination can also form a 15-meter-long robotic arm, which has a wider operating range and can do more scientific research activities.
The Chinese space station mission is divided into three stages: key technology verification, assembly construction and operation, and is currently in the stage of key technology verification. We want to validate many of the techniques of the robotic arm. The weight of the Tianhe core cabin, the Qingtian experimental module, and the Dream experiment module are all more than 20 tons, which means that the mechanical arm must also have the corresponding mobility ability.
Sending astronauts to a specific location outside the cabin is also a complex process, and our robotic arm, like a human arm, consists of 7 joints with 7 degrees of freedom of movement. How these 7 joints are planned for path planning and choose a convenient and safe route also requires special design and consideration.
We also note that Liu Boming also verified the emergency return technology when he first left the cabin. The risk of space operation is high, such as the astronaut standing on the mechanical arm and misoperation, the mechanical arm does not stop moving forward, it is very dangerous, so it must have the ability of astronauts to urgently return to the node module at any time.
Such a precise and complex device as a robotic arm, in the harsh environment of space, must consider the impact of extremely high and low temperatures, space radiation, micro meteors, space debris and so on. There is also a phenomenon of dry friction (also known as "cold welding") in the vacuum environment, if the two metal surfaces are stuck together for a long time, they will stick together and cannot be separated, which is also a technical problem to be overcome.
Q: Is there a risk to astronauts' out-of-the-cabin activities? What guarantees do we make in order to avoid risks as much as possible?
Yang Yuguang: Judging from the development history of manned spaceflight of mankind as a whole, the risk of outgoing activities is indeed extremely high, and the first time mankind went out of the capsule, it encountered serious problems due to the expansion of the space suit due to the pressure difference problem, and it was difficult for astronauts to return to the cabin.
In terms of astronaut protection, extravehicular spacesuits are "protective armor". The U.S. "Gemini" program has also carried out many outgoing activities, the previous few times are not very successful, especially at that time the heat dissipation design of the spacesuit is not very reasonable, there is no ventilation liquid cold suit we just mentioned, when the American astronaut Cernan out of the cabin activity, because the heat in the suit can not be dissipated, the temperature is particularly high, he almost fainted.
In the vacuum of space, the energy radiated by the sun to the size of one square meter is more than 1300 watts, and the spacesuit must reflect this huge energy. Now the space debris situation is getting more and more serious, the trajectory of various tiny space debris is very difficult to predict, if it penetrates the spacesuit, it will cause the space suit to lose pressure and threaten the lives of astronauts. In addition, its pressure maintenance, oxygen supply, in addition to carbon dioxide and harmful gases, humidity and temperature regulation, including power supply, etc. are also very complex, prone to problems, so this aspect to carry out a lot of detailed technical research and sufficient ground experiments.
In an emergency, astronauts should have the ability to quickly (within half an hour) return to the airlock module, which is also the technology related to the verification of the robotic arm just mentioned.
All in all, when we do mission design and space suit design, we must consider various abnormal emergencies to fully protect the safety of our astronauts. However, even if we take a lot of safety measures, the risk of outgoing activities cannot be exactly equal to 0. Because of this, astronauts who can perform spacewalks should be said to be the best among astronauts.
Source: Website of the Central Commission for Discipline Inspection and the State Supervision Commission