1.1 Simulation of weightlessness

Weightlessness, the state of a material body in which the external forces acting on it or the movement it makes do not cause mutual pressure of particles on each other. If a body is at rest in the Earth's gravitational field on a horizontal plane, then the force of gravity and the reaction of the plane directed in the opposite direction act on it, as a result of which mutual pressures of the particles of the body on each other arise. The human body perceives such pressures as a feeling of weight. A similar result takes place for a body that is in an elevator moving vertically down with an acceleration a 1 g, where g is the acceleration of free fall. But when a = g, the body (all its particles) and the elevator are in free fall and do not exert any mutual pressure on each other; as a result, the phenomenon of weightlessness takes place here. In this case, all particles of a body in a state of weightlessness are affected by gravity, but there are no external forces applied to the surface of the body (for example, support reactions) that could cause mutual pressures of particles on each other. A similar phenomenon is observed for bodies placed in an artificial earth satellite (or spacecraft); these bodies and all their particles, having received, together with the satellite, the corresponding initial speed, move under the influence of gravitational forces along their orbits with equal accelerations, as free, without exerting mutual pressure on each other, i.e., they are in a state of weightlessness. Like a body in an elevator, they are affected by the force of gravity, but there are no external forces applied to the surfaces of the bodies that could cause mutual pressures of the bodies or their particles on each other.

In general, a body under the action of external forces will be in a state of weightlessness if: a) the acting external forces are only mass (gravitational forces); b) the field of these body forces is locally homogeneous, i.e., the field forces impart to all particles of the body in each of its positions the same acceleration in magnitude and direction; c) the initial velocities of all particles of the body are the same in modulus and direction (the body moves forward). Thus, any body whose dimensions are small compared to the earth's radius, making free translational motion in the earth's gravitational field, will, in the absence of other external forces, be in a state of weightlessness. The result will be similar for the motion in the gravitational field of any other celestial bodies. Due to the significant difference between the conditions of weightlessness and terrestrial conditions, in which devices and assemblies of artificial Earth satellites, spacecraft and their launch vehicles are created and adjusted, the problem of weightlessness occupies an important place among other problems of astronautics. Weightlessness can be used to implement some technological processes that are difficult or impossible to implement under terrestrial conditions (for example, obtaining composite materials with a uniform structure throughout the entire volume, obtaining bodies of an exact spherical shape from molten material due to surface tension forces, etc.). The first experiment on welding various materials under N. and vacuum conditions was carried out during the flight of the Soviet Soyuz-6 spacecraft (1969). A number of technological experiments (on welding, studying the flow and crystallization of molten materials, etc.) were carried out on the American space station Skylab (1973).

It is especially important to take into account the peculiarity of the conditions of weightlessness during the flight of manned spacecraft: the conditions of a person's life in a state of weightlessness differ sharply from the usual terrestrial ones, which causes changes in a number of his vital functions. Thus, weightlessness puts the central nervous system and receptors of many analyzer systems (vestibular apparatus, muscular-articular apparatus, blood vessels) in unusual conditions of functioning. Therefore, weightlessness is considered as a specific integral stimulus that affects the human and animal organism during the entire orbital flight. The response to this stimulus is adaptive processes in physiological systems; the degree of their manifestation depends on the duration of weightlessness and, to a much lesser extent, on the individual characteristics of the organism.

With the onset of weightlessness, some astronauts develop vestibular disorders. For a long time, a feeling of heaviness in the head area persists (due to increased blood flow to it). At the same time, adaptation to weightlessness occurs, as a rule, without serious complications: in weightlessness, a person retains his ability to work and successfully performs various work operations, including those that require fine coordination or large expenditures of energy. Motor activity in a state of weightlessness requires much less energy than similar movements in weightlessness. If preventive measures were not used in flight, then in the first hours and days after landing (the period of readaptation to earthly conditions), a person who has made a long space flight experiences the following set of changes. 1) Violation of the ability to maintain a vertical posture in static and dynamic; a feeling of heaviness of body parts (surrounding objects are perceived as unusually heavy; there is a lack of training in dosing muscle efforts). 2) Violation of hemodynamics during work of medium and high intensity; pre-fainting and fainting states are possible after the transition from a horizontal position to a vertical one (orthostatic tests). 3) Violation of metabolic processes, especially water-salt metabolism, which is accompanied by relative dehydration of tissues, a decrease in the volume of circulating blood, a decrease in the content of a number of elements in tissues, in particular potassium and calcium. 4) Violation of the oxygen regime of the body during physical exertion. 5) Decreased immunobiological resistance. 6) Vestibulo-vegetative disorders. All these shifts caused by weightlessness are reversible. Accelerated recovery of normal functions can be achieved with the help of physiotherapy and exercise therapy, as well as preliminary training in aircraft to simulate weightlessness, in weightless pools and simulate weightlessness while hovering in the air.

According to the law of universal gravitation, all bodies are attracted to each other, and the force of attraction is directly proportional to the masses of the bodies and inversely proportional to the square of the distance between them. That is, the expression "lack of gravity" does not make sense at all. At an altitude of several hundred kilometers above the Earth's surface - where manned ships and space stations fly - the Earth's gravity is very strong and practically does not differ from the gravitational force near the surface.

If it were technically possible to drop an object from a tower 300 kilometers high, it would begin to fall vertically and with free fall acceleration, just like it would fall from the height of a skyscraper or from a height of human growth. Thus, during orbital flights, the force of gravity is not absent and does not weaken on a significant scale, but is compensated. In the same way as for watercraft and balloons, the force of gravity of the earth is compensated by the Archimedean force, and for winged aircraft - by the lifting force of the wing.

Yes, but the plane flies and does not fall, and the passenger inside the cabin is not flown like astronauts on the ISS. During a normal flight, the passenger perfectly feels his weight, and it is not the lifting force that keeps him from falling to the ground, but the reaction force of the support. Only during an emergency or artificially caused sharp decline, a person suddenly feels that he stops putting pressure on the support. Weightlessness arises. Why? And because if the loss of height occurs with an acceleration close to the acceleration of free fall, then the support no longer prevents the passenger from falling - she herself falls.

spaceref.com It is clear that when the plane stops its sharp descent, or, unfortunately, falls to the ground, then it will become clear that gravity has not gone anywhere. For in terrestrial and near-earth conditions the effect of weightlessness is possible only during the fall. Actually, a long fall is an orbital flight. A spacecraft moving in orbit with the first cosmic velocity is prevented from falling to the Earth by the force of inertia. The interaction of gravity and inertia is called "centrifugal force", although in reality such a force does not exist, it is in some way a fiction. The device tends to move in a straight line (at a tangent to the near-earth orbit), but the earth's gravity constantly "twists" the trajectory of movement. Here, the equivalent of the free fall acceleration is the so-called centripetal acceleration, as a result of which it is not the value of the velocity that changes, but its vector. And so the speed of the ship remains unchanged, and the direction of movement is constantly changing. Since both the ship and the astronaut are moving at the same speed and with the same centripetal acceleration, the spacecraft cannot act as a support on which the weight of a person presses. Weight is the force of the body acting on the support that prevents the fall, arising in the field of gravity, and the ship, like a sharply descending aircraft, does not interfere with falling.

That is why it is absolutely wrong to talk about the absence of terrestrial gravity or the presence of "microgravity" (as is customary in English-language sources) in orbit. On the contrary, the attraction of the earth is one of the main factors of the phenomenon of weightlessness arising on board.

One can speak of true microgravity only in relation to flights in interplanetary and interstellar space. Far from a large celestial body, the action of the forces of attraction of distant stars and planets will be so weak that the effect of weightlessness will occur. About how to deal with this, we have read more than once in science fiction novels. Space stations in the form of a torus (steering wheel) will spin around the central axis and create an imitation of gravity using centrifugal force. True, in order to create the equivalent of gravity, you will have to give the torus a diameter of more than 200 m. There are other problems associated with artificial gravity. So all this is a matter of the distant future.

The weight of a body (substance) is a relative concept. Speaking of weight is a must specify what this weight operates on. It should also be borne in mind that the weight of a body (substance) arises not because the Earth attracts this body, but because there is an air shell (atmosphere) around the Earth. The interaction of air atoms and the atoms of a body surrounded by air causes the appearance of a weight force (gravitational force).

The force of weight arises because the pressure of air atoms exerted on the body from above is greater than the pressure from below (air pressure is the same on the sides).

It is also very important to note here that the force of weight does not depend on the absolute value of the air pressure, but on the difference in pressures above and below the body.

Therefore, the weight of the body will not change if the pressure from above and below is increased by, for example, 10 atmospheres, since the difference will remain the same.

In the case when the difference in pressures from above and below is equal to zero, the body has no weight relative to the air that surrounds it. That is, the body is in weightlessness relative to the surrounding air.

In other words, in a state of weightlessness (for example, an iron ball), the pressure of air atoms on the atoms of the ball (located in its surface layer) is the same from all directions (for example, a pressure of 3 atmospheres acts on each centimeter of the ball's surface).

This condition occurs when the ball is in free fall towards the Earth's surface. In this case, the pressure on the lower part of the ball increases due to the frontal air resistance, and a vacuum is created at the top of the ball.

The change in air pressure on the ball, caused by its movement, leads to the fact that the air pressure on the ball from above and below is equalized. In this case, the pressure difference becomes equal to zero. Accordingly, the weight of the body will also be zero. The body slows down the speed of movement towards the Earth. At the same time, the pressure force caused by the frontal resistance and the discharge force at the top of the ball also decrease. Again, the weight force arises and the process repeats.

Of course, this process is not accompanied by such jumps as I described, it proceeds smoothly. And in the process of free fall of the ball, the forces of air pressure on any area of ​​its surface remain the same.

Therefore, we can say that the weight of a freely falling body relative to the air surrounding it is zero. A ball in free fall is in a state of weightlessness relative to the atmosphere of air surrounding the Earth, and relative to the Earth, the ball has weight.

Now suppose that our iron ball falling in the air is hollow, and its internal volume is filled with air.

This is precisely the same elevator body or spaceship body.

We have already found out that the body will be in zero gravity.

The question arises, will a body (for example, an astronaut) located inside a hollow ball be in weightlessness?

It turns out he will not be in weightlessness. Although the force of its weight will be so small that, compared with the weight of this body on the surface of the Earth, it can be neglected.

In weightlessness, the body inside the spherical cabin of the ship will be in the event that it has the shape of a ball, and is located exactly in the geometric center of the cabin of the ship. At all other points, it will have a small weight.

This little weight will move our balloon towards the inner surface of the larger balloon.

The air pressure in the cavity of a large ball will be distributed in its volume in such a way that the closer we approach the center of the ball, the higher the pressure will be. It will be maximum at the geometric center of the ball. Therefore, a small ball, the geometric center of which will coincide with the geometric center of a large ball, will experience uniform pressure on its surface.

If it is displaced relative to the center in any of the directions, then various pressure forces will act on its surface. This will lead to weight gain.

The difference between these pressures will be small because the ratio of the sizes of the large and small balls is small.

It should also be noted that if the ball is filled not with air, but with water, and an air bubble is used as the body under consideration, then it will always tend to occupy a position in the geometric center of the large ball. This is because the specific gravity of air is less than that of water. I will not talk more about this here.

Before giving a definition of the concept of weightlessness, I will dwell on one more example.

Let's assume that the iron ball lies on the horizontal platform of the Earth.

The weight of the body is the force with which the body, due to attraction by the Earth, presses on a fixed (relative to the Earth) horizontal stand or pulls the suspension thread. The weight of the body is equal to the force of gravity.

Since the support or suspension, in turn, acts on the body, a characteristic sign of weightiness is the presence of deformations in the body caused by its interaction with the support or suspension.

In the free fall of bodies, there are no deformations in them; in this case, the bodies are in weightlessness. The figure shows a setup with which this can be detected. The installation consists of spring scales, to which the load is suspended. The whole installation can move up and down along the guides.

If the scales with the load fall freely, then the scale indicator is at zero, which means that the balance spring is not deformed.

Let's analyze this phenomenon using the laws of motion. Let us assume that a weight suspended on a spring moves down with an acceleration a. Based on Newton's second law, we can say that a force acts on it, which is equal to the difference between the forces P and F, where P is the force of gravity, and F is the elastic force of the springs applied to the load. So,

ma = P - F or ma = mg - F

F = m (g - a)

With a free fall of a load, a \u003d g and, therefore,

F - m (g - a) \u003d 0

This indicates the absence of elastic deformations in the spring (and in the load).

The state of weightlessness takes place not only in free fall, but also in any free flight of the body, when only one force of gravity acts on it. In this case, the particles of the body do not act on the support or suspension and do not receive acceleration relative to this support or suspension under the influence of gravity towards the Earth.

If the installation shown in the figure is made to move freely upwards with a sharp jerk by the rope, then the scale indicator during such a movement will be at zero. And in this case, the scales and the load, moving up with the same acceleration, do not interact with each other.

So, if only one force of gravity acts on the bodies, then they are in a state of weightlessness, a characteristic feature of which is the absence of deformations and internal stresses in them.

The state of weightlessness should not be confused with the state of a body under the action of balanced forces. So, if the body is inside a liquid, the weight of which in the volume of the body is equal to the weight of the body, then the force of gravity is balanced by the buoyant force, But the body will put pressure on the liquid (as on a support), as a result of which the stresses caused in it by gravity will not disappear, but it means that it will not be in a state of weightlessness.

Let us now consider the weightlessness of bodies on artificial earth satellites. During the free flight of a satellite in orbit around the Earth, the satellite itself and all the bodies located on it, in the reference frame associated with the center of mass of the Earth or with “fixed” stars, move with the same acceleration at each given time. The magnitude of this acceleration is determined by the gravitational forces acting on them towards the Earth (the forces of gravitation towards other cosmic bodies can be ignored, they are very small). As we have seen, this acceleration does not depend on the mass of the body. Under these conditions, there will be no interaction between the satellite and all the bodies located on it (as well as between their particles), due to gravity towards the Earth. This means that during the free flight of the satellite, all the bodies in it will be in a state of weightlessness.

Bodies not fixed in the spacecraft, the astronaut himself freely float inside the satellite; the liquid poured into the vessel does not press on the bottom and walls of the vessel, so it does not flow out through the hole in the vessel; plumb bob (and pendulums) rest in any position in which they are stopped.

An astronaut does not need any effort to keep an arm or leg in an inclined position. He loses the idea of ​​where "up" and where "down".

If a body is given a speed relative to the satellite cabin, then it will move in a straight line and uniformly until it collides with other bodies.

In order to eliminate the possible dangerous consequences of the action of the state of weightlessness on the vital activity of living organisms, and above all of man, scientists are developing various methods for creating artificial "gravity", for example, by giving future interplanetary stations rotational motion around the center of gravity. The elastic force of the walls will create the necessary centripetal acceleration, and cause deformations in the bodies in contact with them, similar to those that they had under the conditions of the Earth.

Weightlessness, the state of a material body in which the external forces acting on it or the movement it makes do not cause mutual pressure of the particles on each other. If a body is at rest in the Earth's gravitational field on a horizontal plane, then the force of gravity and the reaction of the plane directed in the opposite direction act on it, as a result of which mutual pressures of the particles of the body on each other arise. The human body perceives such pressures as a feeling of weight. A similar result takes place for a body that is in an elevator moving vertically downwards with an acceleration a ¹ g, where g- acceleration of gravity. But at a =g the body (all its particles) and the elevator are in free fall and do not exert any mutual pressure on each other; as a result, the phenomenon of N. takes place here. At the same time, gravity forces act on all particles of a body in a state of N., but there are no external forces applied to the surface of the body (for example, support reactions) that could cause mutual pressures of particles on each other. friend. A similar phenomenon is observed for bodies placed in an artificial earth satellite (or spacecraft); these bodies and all their particles, having received, together with the satellite, the corresponding initial velocity, move under the action of gravitational forces along their orbits with equal accelerations, as free, without exerting mutual pressure on each other, i.e., they are in the state H. As well as on the body is in an elevator, they are affected by the force of gravity, but there are no external forces applied to the surfaces of the bodies that could cause mutual pressures of the bodies or their particles on each other.

In general, a body under the action of external forces will be in the state of N. if: a) the acting external forces are only mass (gravitational forces); b) the field of these body forces is locally homogeneous, i.e., the field forces impart to all particles of the body in each of its positions the same acceleration in magnitude and direction; c) the initial velocities of all particles of the body are the same in modulus and direction (the body moves forward). Thus, any body whose dimensions are small compared to the earth's radius, making free translational motion in the Earth's gravitational field, will, in the absence of other external forces, be in the state H. The result will be similar for motion in the gravitational field of any other celestial tel.

Due to the significant difference between the conditions of N. from terrestrial conditions, in which devices and units of artificial Earth satellites, spacecraft and their launch vehicles are created and debugged, the N. problem occupies an important place among other problems of astronautics. This is most significant for systems that have tanks partially filled with liquid. These include propulsion systems with liquid-propellant rocket engines, designed for repeated switching on in space flight conditions. Under N. conditions, the liquid can occupy an arbitrary position in the container, thereby disrupting the normal functioning of the system (for example, the supply of components from fuel tanks). Therefore, to ensure the launch of liquid propulsion systems under N. conditions, the following are used: separation of the liquid and gaseous phases in fuel tanks with the help of elastic separators (for example, on the Mariner AMS); fixing part of the liquid at the intake device with a grid system (Agena rocket stage); the creation of short-term overloads (artificial "gravity") before turning on the main propulsion system with the help of auxiliary rocket engines, etc. The use of special methods is also necessary for separating the liquid and gaseous phases under N. conditions in a number of units of the system life support, in fuel cells of the energy supply system (for example, collection of condensate by a system of porous wicks, separation of the liquid phase using a centrifuge). Spacecraft mechanisms (for opening solar panels, antennas, for docking, etc.) are designed to work in N.

N. can be used to implement certain technological processes that are difficult or impossible to implement under terrestrial conditions (for example, obtaining composite materials with a uniform structure throughout the volume, obtaining bodies of an exact spherical shape from molten material due to surface tension forces, etc.). The first experiment in welding various materials under N. and vacuum conditions was carried out during the flight of the Soviet Soyuz-6 spacecraft (1969). A number of technological experiments (on welding, studying the flow and crystallization of molten materials, etc.) were carried out on the American Skylab orbital station (1973).

It is especially important to take into account the uniqueness of the conditions of N. during the flight of manned spacecraft: the conditions of life of a person in a state of N. differ sharply from the usual terrestrial ones, which causes changes in a number of his vital functions. So, N. puts the central nervous system and receptors of many analyzer systems (vestibular apparatus, muscular-articular apparatus, blood vessels) in unusual conditions of functioning. Therefore, N. is considered as a specific integral stimulus that acts on the human and animal organism during the entire orbital flight. The response to this stimulus is adaptive processes in physiological systems; the degree of their manifestation depends on the duration of N. and to a much lesser extent on the individual characteristics of the organism.

With the onset of N.'s condition, some astronauts develop vestibular disorders. For a long time, a feeling of heaviness in the head area persists (due to increased blood flow to it). At the same time, adaptation to N. occurs, as a rule, without serious complications: in N. a person retains his ability to work and successfully performs various work operations, including those that require fine coordination or large expenditures of energy. Motor activity in the state of N. requires much less energy costs than similar movements under conditions of gravity. If preventive measures were not used in flight, then in the first hours and days after landing (the period of readaptation to earthly conditions), a person who has made a long space flight experiences the following set of changes. 1) Violation of the ability to maintain a vertical posture in static and dynamic; a feeling of heaviness of body parts (surrounding objects are perceived as unusually heavy; there is a lack of training in dosing muscle efforts). 2) Violation hemodynamics during work of medium and high intensity; pre-fainting and fainting states are possible after the transition from a horizontal position to a vertical one (orthostatic tests). 3) Violation of metabolic processes, especially water-salt metabolism, which is accompanied by relative dehydration of tissues, a decrease in the volume of circulating blood, a decrease in the content of a number of elements in the tissues, in particular potassium and calcium. 4) Violation of the oxygen regime of the body during physical exertion. 5) Decreased immunobiological resistance. 6) Vestibulo-vegetative disorders. All these shifts caused by N. are reversible. Accelerated recovery of normal functions can be achieved with the help of physiotherapy and exercise therapy, as well as the use of drugs. The adverse effect of N. on the human body in flight can be prevented or limited by various means and methods (muscle training, muscle electrical stimulation, negative pressure applied to the lower half of the body, pharmacological, and other means). In a flight lasting about 2 months (the second crew at the American station Skylab, 1973), a high preventive effect was achieved mainly due to the physical training of the cosmonauts. High-intensity work, which caused an increase in heart rate up to 150-170 beats per minute, was performed on a bicycle ergometer for 1 hour a day. Restoration of the function of blood circulation and respiration occurred in cosmonauts 5 days after landing. Changes in metabolism, stato-kinetic and vestibular disorders were weakly expressed.

An effective means would probably be the creation of an artificial "gravity" on board the spacecraft, which can be obtained, for example, by making the station in the form of a large rotating (i.e., not moving forward) wheel and locating the working rooms on its "rim". Due to the rotation of the "rim" of the body in it, they will be pressed against its side surface, which will play the role of the "floor", and the reaction of the "floor" applied to the surfaces of the bodies will create artificial "gravity". The creation on spacecraft of even a small artificial "gravity" can ensure the prevention of adverse effects of N. on the organism of animals and humans.

To solve a number of theoretical and practical problems of space medicine, laboratory methods for modeling N. are widely used, including limiting muscle activity, depriving a person of his usual support along the vertical axis of the body, reducing hydrostatic blood pressure, which is achieved by staying a person in a horizontal position or at an angle (head below the legs), prolonged continuous bed rest or immersion of a person for several hours or days in a liquid (so-called immersion) medium.

Lit.: Kakurin L. I., Katkovsky B. S., Some physiological aspects of long-term weightlessness, in the book: Results of Science. Series Biology, c. 8, Moscow, 1966; Medico-biological research in weightlessness, M., 1968; Physiology in space, trans. from English, M., 1972.

S. M. Targ, E. F. Ryazanov, L. I. Kakurin.