Is artificial gravity difficult? To solve the problem that astronauts can’t stand up, why doesn’t the space station simulate gravity?

At 13:34 on September 17, 2021, Shenzhou-12 landed at the Dongfeng Landing Field in Inner Mongolia with unprecedented precision. Search and rescue personnel arrived at the scene about 3 minutes after landing. The entire mission has reached the spacecraft The extreme that recycling can achieve has also attracted the attention of the global aerospace industry.

Later, the astronauts were interviewed at the spacecraft landing site, which was also the welcome ceremony for the astronauts returning to Earth. However, I believe there was a scene that deeply hurt everyone. The astronauts who returned to Earth were all sitting on chairs. on board, and at other recovery sites, astronauts were even carried to the logistics vehicle.

Friends who are familiar with aerospace medicine know that this is a common phenomenon caused by long-term weightlessness in spacecraft and space stations. Almost all astronauts need a relatively long adaptation process to return to Earth. The longer they stay in the sky, the The recovery time is also longer! It seriously affects life and work. Can a gravity environment be simulated in the sky? Make future space station missions as easy as a business trip!

Weightlessness is fun. Flying around and carrying heavy objects shouldn’t be too easy, but in fact the astronauts are not in the mood to play! And if you stay in this environment for a long time, it will have a considerable impact on the human body:

First of all, the position sensor of the human vestibular organ fails, which will cause very serious dizziness, but this problem will be almost the same after adapting to it. Now, the more troublesome thing is later. There are several problems with long-term weightlessness. The first is stretching your body. Even if you lie down on the earth, it is difficult, but weightlessness will not happen, and the muscles do not need to maintain tension.

So muscle atrophy will occur. The second serious problem is the reduction of blood and red blood cells! Because body fluids are redistributed after weightlessness, and when running to the upper body, the body will automatically adjust body fluid function when it feels that there is more blood. However, the reduction of total blood volume and red blood cells can cause cardiac dysfunction such as arrhythmia and even myocardial hypoxia.

Others can also lead to a decrease in immunity, making it easier to get sick than on earth. Weightlessness can also easily lead to a large loss of calcium, etc. Of course, exercising in space can solve the problem of muscle atrophy. Use negative pressure pants. It can also solve the problem of reduced blood volume, and drugs can also be used to supplement calcium and improve immunity. However, these methods can only improve but cannot completely solve it. Isn't there a once and for all solution?

Speaking of simulating a gravity environment, you must remember that a centrifugal gravity module on the International Space Station was cancelled. What is its principle and why was it cancelled?

The gravity module of the International Space Station is only in the plan and has not even been implemented. Its principle is to use centrifugal force to simulate the gravity environment. However, due to the relatively small structure, it cannot be manufactured due to the diameter of the rocket fairing. It was too big, so the cabin was canceled after evaluation, but at least it told everyone that it is possible to create artificial gravity in space!

How many possibilities are there for simulating a gravity environment?

The gravity environment is very special. A phenomenon that is common on the earth does not exist in the space station. The centrifugal force generated by orbiting the earth here is equal to gravity, so it is in a state of weightlessness or microgravity. Generally speaking, in There are several ways to simulate gravity under weightlessness:

1. Continuously accelerate with an acceleration of 1 G or continuously decelerate with an acceleration of 1 G

2. Use centrifugal force to simulate a gravity environment ;

3. Create a gravity field to reconstruct the gravity environment;

The first one will encounter overload when the rocket is launched or when the spacecraft returns to the earth. The former is caused by acceleration, and the latter The other is caused by decelerating too fast, but the problem is that one needs to continue to accelerate, and the other needs to continue to decelerate. The former will approach the speed of light in about a little more than a year!

So it seems that you can play like this, keep accelerating, and then when it reaches the speed of light, turn around and keep decelerating, and then repeat! It is estimated that in order to simulate gravity, I don't know how much fuel will be consumed. No matter how rich I am, I can't burn it like this, so it won't work.

In science fiction films, you can often see people standing directly on the spacecraft. Theoretically, it is possible to create a gravity field on the spacecraft, but for now, the gravity environment requires a mass of nearly To achieve it, for example, if the earth is so big, it can provide a gravity environment of 1 G and carry the earth with it? Why do you need a spaceship? Apart from this, it seems difficult to imagine any other technology that can achieve this.

In the end, only the "centrifugal force" simulation method is left

Everyone knows the "centrifugal force" method. For example, on the acrobatic field, the motorcycle can rotate in a huge vertical ring. Driving inside the inner wall uses "centrifugal force", so it can be achieved by building a simulated gravity cabin similar to the International Space Station. The structure is simple, and you only need to adjust the rotation speed to determine how much gravity you want!

But here comes the problem. When a person stands on a centrifugal structure simulation, the general understanding is that the head points to the center of rotation, and the feet are perpendicular to the tangent direction of the contact point. At this time, you will find a problem. The centrifugal force received is different from the position of the sole of the foot. Therefore, at this time, there is a difference between the position and state felt by the vestibular organ and the state under the feet, which will be very uncomfortable.

The other reason is that the size of the simulated gravity environment is not large enough, so if you want to have enough centrifugal force to simulate the gravity environment, you need a relatively high speed. At this time, the displacement of the vestibular organ will also be obviously felt. As well as changes in spatial position, you will soon become dizzy. If you stay in this environment for a long time, you will probably go crazy!

How big a structure is needed to use centrifugal force to simulate a comfortable gravity environment?

Therefore, there must be a large enough environment to simulate the gravity environment. So how big is the structure? This can be calculated. For example, the human vestibular organ has a clear sense of rotation, so it must be slower. If it exceeds three revolutions per minute, it will feel uncomfortable, so the speed should be controlled at 1.5~2 revolutions per minute. The other is the gravity environment. We don’t need to simulate 1:1 gravity, only 0.5G is enough. Then we only need to calculate as follows:

A 0.5G environment is: 4.9M/S^2

The w requirement is 2 revolutions/minute, which is converted into radians of about 0.2094395 radians/second

Then it can be concluded that the required radius is R=111.7M

Everyone But look carefully, this is the radius! It is wider than the International Space Station (the length of the International Space Station is the size of the solar wing and the width is the size of the cabin), so if you want to achieve a gravity environment in space, you have to build a space station with a diameter of about 220 meters.

What structure is better to use?

The circular shape is obviously the most suitable, and the central symmetry also looks beautiful. For example, the "Hermes" spacecraft in "The Martian" has a circular living cabin in the middle. It can provide a gravity environment on the way from Earth to Mars.

The "Eternity" in "Interstellar" is a ring with multiple cabins connected. After all, aerodynamic shape does not matter in space. As long as sufficient centripetal acceleration can be achieved, then it only needs to be rotated during rotation. Just balance it.

Another typical structure is the long rod in "Avatar". Its center is located on the axis of the "Entrepreneurship Star" and revolves at a speed of 2-3 circles per minute. Running, the length of the crossbar can be reduced at such speed, but this will sacrifice comfort or reduce gravity acceleration.

The "Avalon" in "Passengers" is in the shape of an overall spiral. When the spacecraft flies, it rolls to simulate gravity.

The four structures are all relatively good, but the first two structures, a ring with a diameter of 220 meters and a circumference of 691 meters, are obviously a super project, and the last one, "Avalon" "A spaceship is obviously not something that humans can manufacture with current technology, so the easiest thing to implement under the current situation is a long-pole simulated gravity cabin.

For example, if the requirements are lowered and only a 0.2G environment is required, and the rotation speed is about 2 turns, the gyration radius of the long rod can be reduced to 44.68 meters, which means the length of the long rod is about 89 meters. Basically, the current International Space Station can meet the requirements if it rotates!

Of course, the space station is not unable to rotate, it is just not designed according to the structure of rotation to generate gravity. If a gravity environment is to be generated, it must be specially designed for the gravity environment. The cabin along the long pole design gradient simulates the gravity environment. The closer to the middle, the weaker the gravity becomes. The closer to the two ends, the stronger the gravity. The maximum "gravity environment" is 0.2G at the top of the long pole.

Why do we need ring-shaped and long-rod types? Can spherical ones work?

In an environment where gravity is simulated, the spherical shape is not a suitable shape. Except for the appropriate simulated gravity at both ends at the "equator" position, other positions will produce "force components that are not perpendicular to the floor." ", for example, refer to the Ceres space station in "The Expanse", which has to tilt far away when pouring water.

In fact, as early as the "Age of Space Navigation" in the 1970s and 1980s, super circular space stations were already planned and designed, including long cylindrical ones and super circular ones, as shown in "Elysium" The space station has been imagined by scientists in the last century, and it is really spectacular.

But for now, the long rod shape is the closest to reality, and its implementation cost is also the lowest! The long rod does not need to be designed with a mechanical seal rotating device around the center (future docking will be very troublesome, and it can be stopped before docking), or it can be designed with a central cabin structure, using a connecting mechanism to keep the center from rotating, but there will be problems connecting the mechanical structure. Problem, obviously the former has a simple structure.

Further reading: How to create a zero-gravity environment?

The gravity environment does not need to be simulated on the ground. Instead, the zero-gravity environment must be simulated for training and experiments. Generally, there are several ways to realize the modern zero-gravity environment, one is free fall, the other is Use the aircraft to maintain a certain rate of ascent and descent when jumping to a high altitude and then descending to simulate a weightless environment.

The former time free fall time can be calculated based on the altitude, the latter can also be calculated based on the aircraft's jump curve and limit ceiling, but obviously the time is relatively short (using an aircraft simulation time is longer), Moreover, the cost of zero-gravity simulation is relatively high. For example, the price of a zero-gravity flight in Europe is more than 6,000 US dollars per person!