Aviation trivia: Why do astronauts have to sit in chairs after returning to the cabin?

To say which profession in our various industries has the highest risk, the highest altitude, and the fastest speed, of course, it is astronauts. Their operating altitude has exceeded the earth in a sense, and the speed has even reached an astonishing 7.9 Km/sec, which is the first cosmic speed. And astronauts are also the only profession that needs to be separated from the earth’s living environment. No matter how reliable the current manned space equipment is, it is a risk to let a creature leave the environment where it depends.

Astronauts represent human beings to explore the unknown outer space. Unexpected dangers may occur at any time during this journey. Therefore, to become an astronaut, you must have excellent mental and physical qualities, extraordinary courage, and the spirit of seeing death at home. As well as strong professionalism, only in this way can we complete and write established scientific research missions in space, complete corresponding instructions and operations, and deal with emergencies calmly and calmly. So every astronaut returning from space is a hero of mankind, but we have also discovered this phenomenon, that is, astronauts of various countries first sit on chairs and accept people’s welcome after they exit the capsule on the ground. Why? This is actually related to the difference between space and ground environment.

Microgravity environment near earth orbit

Any object that exists on the surface of the earth, including all living things, has been in a gravity environment of 1G since its birth. Not only that, the ancestors of our biological world also reproduced in such an environment during the process of evolution. Therefore, the various functions of our body are adapted to this gravitational environment. And the existence of gravity also gives us human sense of direction and balance. We think that downward always points to the direction of gravity, while upward is just the opposite of gravity. With up and down, there are front, back, left, and right.

I believe you have also heard of the concept of “weightlessness”. In fact, an object will not receive any acceleration, that is, it will not receive any net external force. Einstein’s equivalent principle tells us that gravity is actually the same as acceleration. But it is difficult for us to find a place of perfect weightlessness on the earth or in the universe within the reach of mankind. More or less weak acceleration will be felt, so we call it a microgravity environment.

Generally, we humans want to create a microgravity environment in four ways: tower drop, airplane, rocket and spacecraft. Tower falling is actually a kind of free fall movement. Due to the limitation of distance, it is usually timed in seconds. The longest time is currently 10 seconds, which can produce a microgravity level of 10^-4~10^-6G; aircraft can choose to fly parabola, To generate a microgravity environment, first climb upwards, all personnel in the aircraft will feel the acceleration of 2G, then level flight and finally dive down so that it can produce 20 seconds. With a microgravity level of 10^-2G, rockets are actually the same as airplanes.

The last type of spacecraft orbiting the earth is the most ideal microgravity experiment environment for human beings. It lasts for a long time and the perceived acceleration of gravity is low. You may want to ask: Why does the spacecraft produce weak acceleration in the earth’s orbit? ? That is why does it feel power? It is not that gravity and centrifugal force (inertial force) balance each other. In fact, it is difficult to have a perfect environment in the vacuum environment of space. Spacecraft will also be perturbed by atmospheric drag and the gravitational forces of other celestial bodies during their orbits near the earth, which will give the spacecraft a tiny acceleration. As a result, the spacecraft loses its operating speed, which is why we regularly provide power to spacecraft operating near the earth’s orbit.

The impact of microgravity environment on people

In fact, the importance of gravity to life has been mentioned above. The human body will have various uncomfortable, nauseous, and headache performances under the condition of gravity disorder. For example, if you ride a roller coaster and constantly change your movement posture, The acceleration of gravity will also change, sometimes overweight and sometimes weightless. The final result is that the person’s gravity sensing system and balance system are disturbed. The brain thinks that the body is poisoned, so it sends out the command to vomit.

However, this kind of weightless environment is something that astronauts must adapt to, because they have to eat, wear, shelter, and travel in such an environment. People who faint after a few turns are definitely not suitable for flying airplanes, and even less suitable for astronauts. In addition to these, the microgravity environment can also have adverse effects on the human body, including:

Impact on the circulation of blood and body fluids: The flow of various fluids in our body has adapted to the 1G gravity environment, that is to say, the human circulatory system has evolved for this gravity environment. If you lose gravity, a lot of blood and body fluids will rush to the upper body, especially the neck and head. Causes congestion of the sinuses, no ventilation, swelling and puffiness of the face, swelling of neck veins. This will cause dizziness, headache, and dizziness in the long term.

Effects on bones: Long-term exposure to microgravity will cause metabolic disorders in the human body, reduce the synthesis of some proteins, reduce immunity, and affect the body’s absorption of calcium, and also lead to the loss of calcium in bones. Therefore, the bone density of people who have been exposed to microgravity for a long time will decrease and fractures will easily occur.

Effect on muscles: This is best understood. In a microgravity environment, you can’t feel your weight at all, and you can’t feel the weight of your arms and legs. You can move quickly in the space capsule by gently scratching the inner wall. , The long-term complete relaxation of the muscles will cause muscle atrophy, weakness, and soreness.

Why make a stool?

In fact, the most important thing is the long-distance travel, an adaptation process from a microgravity environment to a gravity environment. Normal people lie on the bed for a few days, completely relaxed, and have weak legs and dizziness when they stand up suddenly on the bed together. Not to mention how astronauts feel when they return to Earth after staying in space for a few days. They need to be helped out of the warehouse and sit down quickly. Standing up might really make their legs fall or faint.

Especially those astronauts who work for a long time on the International Space Station, although they will use equipment to exercise muscle strength in the space capsule, they also need to sit on a chair when they return to Earth, and are carried away, and immediately sent to the hospital for rehabilitation. So it’s not that the astronaut wants to sit, but that he can’t stand up, or it’s too tired to stand.