Can an expert talk about the principle of spacewalk and its relationship with gravity? Can you speak more clearly?

1. Is it difficult for astronauts to fall asleep under weightlessness? This is a problem worth discussing, because there are many reasons that affect sleep. First of all, it is necessary to distinguish whether astronauts work in space in one shift or two shifts. On the International Space Station and most space shuttles, all astronauts sleep at the same time. They hang their sleeping bags in places they like to sleep, such as walls, corners and ceilings. When astronauts work in shifts, like some space shuttles, including space laboratories, astronauts sleep in a small bunk, which can be closed to isolate the noise from the studio. At first, the astronauts felt uneasy, feeling that they were lying in a narrow shoe box, and most astronauts had the illusion that their backs felt comfortable for 1-15 seconds. However, when you are going to sleep, you need to get used to feeling nothing on your back and side. In fact, you are floating in a sleeping bag, just hanging you upside down with a rope, so the feeling of gravity that makes you sleepy does not exist, and some astronauts are not used to it. They are so sleepy that they have to take sleeping pills to fall asleep. Others can sleep soundly even in this special environment. What needs to be added is that if your head is in an unventilated place when you sleep, the exhaled carbon dioxide will gather near your nose. When the carbon dioxide in your blood reaches a certain level, an alarm system in the back of your head will give you a warning, which will wake you up and make you feel short of breath. At this time, if you walk a few steps or change places, you can sleep again. 2. Do astronauts have any special feelings when they wear clothes in space? Astronauts' spacesuits are usually no different from what we wear on earth except for special requirements on comfort and safety. For example, clothes must be made of fireproof materials. When wearing a spacesuit in weightlessness, astronauts actually float in the clothes. Only when the clothes touch the skin will they feel that they are wearing clothes. 3. Is it interesting to float in space? Astronauts agree that it is very interesting to float in space once they adapt to the microgravity environment. By the way, scientists don't like to call microgravity zero gravity, because unless you happen to be standing in the center of a spacecraft that is in free fall around the earth, you will inevitably be influenced by tiny accelerations and tides. Even if their effects are very small, only one millionth of the gravity of the earth, we can't consider it zero gravity or zero gravity. This is why we call it weightlessness. Living in microgravity is very interesting, and different people feel different. Astronauts who take part in space flight for the first time, about 3%-4% of them have "space adaptation syndrome" (it is a kind of motion sickness) in the first two or three days after entering space, and others will not have this symptom. Blood flows to the upper body, making the sinuses and tongue congested, affecting people's feelings. In a week or so, astronauts will have a reaction to adapt to weightlessness. In the case of weightlessness, the spine becomes longer because there is no gravity, which makes people taller (1-2 inches taller). In weightlessness, when all muscles are relaxed, there will be a slight upward lift of thighs, arms spread forward to Fang Shu, and a slight bow of the body, as if in water. Because there is no feeling of "up" or "down", we need to rely on other signs to determine "up" and "down". In the internal design of the space shuttle, we should consider using the difference between the ceiling and the floor to locate it. In microgravity, astronauts often have illusions. When an astronaut tells his brain which direction is "up", it will immediately think that it is an illusion. In this way, positioning, moving or moving in space feels different from that on the ground. Walking in space is very easy, and astronauts soon get used to walking around and fixing themselves on the space station with fixed feet. It is much more difficult to walk in space with a spacesuit. This is because the overalls are bulky, just like putting on a balloon, and the vision and touch are limited. 4. How long can you wear a space suit? You can usually wear it for 5-7 hours. Of course, it also depends on the consumable materials in the space suit, such as oxygen, electricity and cooling water. The spacesuit is simply a small spaceship, and it is very hard to work in it. The wearing time is also related to the wearer's requirements for comfort and wear resistance. 5. What should I do if I encounter a fracture or serious illness in space? Fortunately, NASA's 12 astronauts have never encountered such a situation. In the early days, there were problems of urine infection and small-scale influenza in Apollo 13 astronaut Fred. Spaceships always carry enough medicine to deal with these emergencies. Once an accident happens during the flight around the earth, whether on the space shuttle or on the International Space Station, astronauts should be sent back to the earth as soon as possible. NASA has also developed a large seven-seat return capsule for the International Space Station, which is used as a "space ambulance" under special circumstances. In the event of a fracture, equipment for fixing bones is also prepared on the spacecraft. When humans leave for outer space, such as exploring Mars, the spacecraft will carry medical equipment. One or more astronauts are trained in medical knowledge, and they can carry out rescue and treatment. Because in this case, it is impossible to return to earth in a short time. If possible, the ship will be equipped with experienced doctors. 6. How many people can the space station hold? The International Space Station can accommodate up to seven astronauts. The number of astronauts increased from 3 at the beginning to 6, and increased to 7 in 23. Of course, it is impossible for all the staff to return immediately in an accident. That's why NASA has to improve the return capsule so that it can accommodate more people than the Russian Soyuz spacecraft. 7. How do astronauts on the space station spend their spare time in space? They have different preferences according to their own preferences. During the flight, they can choose their own favorite entertainment. Some can use laptops to read books or send emails to their families, some are listening to music or playing games, and some are just talking to relatives and friends on the ground or chatting with other colleagues. However, when most astronauts first entered the space station, they spent most of their spare time standing by the window, looking out at the universe and watching the earth disappear from under the space station. 8. How were the astronauts of the International Space Station selected? What do you think of this? Any adult men and women who are in good health and meet the basic requirements of astronauts can be selected to participate in astronaut training. To become a mission expert or astronaut on the International Space Station, the minimum requirement is to obtain at least a bachelor's degree in engineering, natural science or mathematics from a nationally recognized institution, with more than three years of relevant work experience in this field, and a higher degree will be more suitable. Shuttle pilots must have at least 1 hours of jet flight experience, and their eyesight is better than that of experts. Competition is fierce, with an average of 4, applicants competing for 2 places every two years. Recruit astronauts regularly. 9. How do you draw the space map? How do you know which direction to go? Let me briefly introduce that it is not easy to fully understand this complicated problem, because you really need to enter the university for systematic study. The most basic thing is that you need to know that the universe is composed of three spaces, so you should determine your exact position in the coordinate system composed of these three axes. In the field of astronomy, astronauts use azimuth, altitude, right ascension, distance and time to draw space maps. When flying in space, our three coordinates are calibrated as x, y and z. Then all people have a consistent reference system, that is, the position and direction of the coordinate system, to measure and locate. Generally, this system takes the center of the earth as the origin. On the z axis, the x axis and the y axis are on the same plane. Sometimes it can be assumed that it rotates with the earth, and sometimes it is fixed in space. This "reference system" can also be loaded on your portable computer. Spacecraft (and all large aircraft now) are equipped with a navigation system, which can know the movement of flying objects near its three coordinates and constantly calculate the changes of the spacecraft relative to the reference system. Of course, by looking at the designated target, we can also predict its direction. And soon, you will know where you are and where you are going. If you deviate from the set route, you can consider making corresponding adjustments. 1. What kind of tableware do astronauts use to eat in space? Are they any different? Ordinary tableware is used in space flight, such as knives, forks and spoons, which are the same as those used on earth. Most of the food and drinks eaten by astronauts can be put in containers. The difference is that when these foods are eaten, they will float out. Some foods, such as peas and beans, should be added with sauce so that they will stick to the tableware. Food is hot, cold or frozen. Drinks are packed in some squeezable bottles, like sports drinks bottles. However, some things are difficult for astronauts to adapt to. They often complain that they can't get fresh vegetables and fresh coffee during long-term missions. By the way, in the Mir space station in Russia, once the transported space shuttle arrives, you can get fresh fruits and vegetables like tomatoes. American astronaut Shannon Lucid said that they often get together with Russian astronauts. Maybe in a few years, we will be able to eat fresh vegetables on the International Space Station and the Mars expedition. At present, there is no guarantee to provide fresh coffee and soda, but at least one soft drink company has begun to develop a container for use in weightlessness. In addition, because of the transfer of body fluids in space flight, astronauts' taste and sense of smell have changed, and astronauts in orbit often choose heavy food. 11. How long will the astronauts stay on the International Space Station? Most astronauts have to stay on the International Space Station for 9 consecutive days-that's the average time of "rotation" in the current astronaut program. Some people come back early for various reasons, and others may stay for a long time, especially when they want to provide a basis for human exploration of Mars and fly for a long time to conduct medical research on the life and work of astronauts. It is worth mentioning that the person who stayed in space for the longest time was a Russian physician, Dr. Valery Polyakov, who set this record in 1994, staying in the space station for 438 days (14 1/2 months), and the previous flight record of 241 days was set in 1988. The longest time for Americans to live in space is 188 days, which is also a world record for female astronauts. It was created by Dr. Shannon Lucid. 12. Why does the earth have gravity but not in space? There is gravity in space, but I know you don't mean this. It can be explained that the generation of gravity is related to mass. Mass affects space in a very special way (Einstein would say that mass bends space. ) This effect is transmitted by the force discovered by Isaac Newton, which we call gravity. According to our observation, the theory of universal gravitation is correct. If this were not the case, the Apollo moon landing program would not be realized. Similarly, the decrease of gravity of an object is proportional to the square root of the distance between objects. On the earth, the gravity produced by the mass of an object acts like a "pressure" on the object in contact with the ground, which we call "weight". When there is no such contact, for example, in the earth orbit, the aircraft is not in direct contact with the earth, so there is no gravity. But if the spacecraft still has mass, it will produce its own gravity zone (of course, there is no gravity for a small space shuttle). That is to say, all the stars with great mass centers in space, such as the sun, the earth and other planets, have gravity. Newton also found that objects in vacuum can move in a straight line without acceleration. However, an object, such as a space station, cannot be considered to be in a "weightless" state when the earth pulls it and makes it run in the earth orbit; In this way, the "weightlessness" of the orbiting space station is not the absence of gravity, but the disappearance of gravity. Once there is resistance, atmospheric resistance, engine power, centrifugal acceleration caused by rotation, etc., weightlessness disappears. 13. How did the space shuttle feel when it was launched? On the launch pad, because of the direction and position of the cockpit, the astronauts are back to back with their feet up (the space doctor stipulated the time when they were in this state before launch). After the hatch was closed and all the final inspections were completed, the astronauts silently looked forward to the launch, and once again recalled the operating procedures they had trained in the past few years. For example, are all the cabinets above them locked? The prompt card in front of you reminds you what to do in an emergency. Finally, the countdown to 6 seconds, three liquid rocket propulsion lit. When the space shuttle rocked back and forth for 5 feet, you could obviously feel its shaking. At this time, the orbiter oscillated and vibrated strongly. But the astronauts couldn't hear the thunder of any engine. Then the count reached zero, and the instructions came from the wireless device on the helmet: "Ignition, take off." Two solid fuel rocket propellers ignited and the space shuttle began to rush into space. At this time, you won't feel the obvious acceleration, which is similar to the feeling when the plane takes off. The fuel in the rocket propeller does not burn evenly, and it bumps badly during propulsion. The whole cockpit is like a car speeding on pebbles at maximum speed. Once the thrusters are lit, they won't stop until the fuel burns out. Two minutes after take-off, the empty container of the space shuttle began to fall off, the noise disappeared, and the discomfort of each astronaut was greatly reduced. The fuel in the engines of the three liquid propellers continued to burn and hum. When the fuel was burned out, the space shuttle became lighter and continued to maintain its acceleration. (Because according to Newton's theory, acceleration is equal to the square of mass. 7.5 minutes after liftoff, 9% of the fuel in the huge external container has been burned, and the weight of the space shuttle reached 2, tons when it took off, but now it is less than 2 tons, and the pressure has reached 3 g-three times the gravity of the earth. The engine decelerated to 3g's. At this acceleration, it is very difficult for astronauts wearing heavy spacesuits to breathe, and they will subconsciously breathe and hold out their chests. Finally, the main engine is turned off. Within a few seconds, the propulsion of the engine dropped to zero. Astronauts will suddenly feel the pressure on their chests disappear and feel weightless. At this time, astronauts are already in space. 14. Why should we build a space station? What is its use? There are many reasons why our country proposes to build a permanent platform in earth orbit, and we can benefit a lot from international cooperation with other countries. The space station provides a brand-new way to improve people's living standards. Now everyone should know that in the earth's orbit, space provides many very useful environments that can't be found on the earth, such as weightlessness, high vacuum, high temperature, extremely cold and extremely hot.