Simple questions. A book similar to an encyclopedia Antonets Vladimir Alexandrovich

Why don't satellites fall to Earth?

The answer to this question is given in school. At the same time, they usually also explain how weightlessness arises. All this is so inconsistent with intuition, based on the experience of earthly life, that it does not fit well in the head. And therefore, when school knowledge disappears (there is even such a pedagogical term - “residual knowledge”), people again wonder why the satellites do not fall to Earth and weightlessness occurs inside the spacecraft during the flight.

By the way, if we can answer these questions, then at the same time we will clarify for ourselves why the Moon does not fall on the Earth, and the Earth, in turn, does not fall on the Sun, although the gravitational force of the Sun acting on the Earth is huge - about 3, 6 billion billion tons. By the way, a person weighing 75 kg is attracted by the Sun with a force of about 50 g.

The movement of bodies with very high accuracy obeys the laws of Newton. According to these laws, two interacting bodies, which are not affected by any external forces, can be at rest relative to each other only if the forces of their interaction are balanced. We manage to stand motionless on the earth's surface because the force of the earth's gravity is exactly compensated by the force of the pressure of the earth's surface on the surface of our body. At the same time, the Earth and our body are deformed, due to which we feel heaviness. If, for example, we begin to lift some kind of load, we will feel its heaviness through muscle tension and body deformation, through which the load rests on the ground.

If there is no such compensation of forces, the bodies begin to move relative to each other. This movement always has a variable speed, and both the magnitude of the speed and its direction can change. Now imagine that we have dispersed some body, directing its movement parallel to the surface of the Earth. If the starting speed was less than 7.9 km / s, that is, less than the so-called first cosmic speed, then under the influence of earth's gravity, the speed of the body will begin to change both in magnitude and in direction, and it will certainly fall to the Earth. If the acceleration speed was more than 11.2 km / s, that is, the second space velocity, the body will fly away and never return to Earth.

If the speed was greater than the first, but less than the second cosmic speed, then when the body moves, only the direction of the speed will change, and the value will remain constant. As you understand, this is possible only if the body moves in a vicious circle, the diameter of which is the greater, the closer the speed is to the second cosmic one. This means that the body has become an artificial satellite of the Earth. Under certain conditions, the movement will occur not along a circular, but along an elongated elliptical trajectory.

If a body in the region of the Earth is dispersed in a direction perpendicular to the segment connecting the Earth with the Sun, up to a speed of 42 km / s, it will forever leave the solar system. The Earth has an orbital speed of only 29 km / s, so, fortunately, it can neither fly away from the Sun nor fall on it and will forever remain its satellite.

Today, we can step outside our home in the early morning or evening and see a bright space station fly overhead. Although space travel has become a regular part of the modern world, for many people space and the issues associated with it remain a mystery. So, for example, many people do not understand why satellites do not fall to Earth and fly into space?

elementary physics

If we throw a ball into the air, it will soon return to Earth, just like any other object, such as an airplane, a bullet, or even a balloon.

To understand why a spacecraft is able to orbit the Earth without falling, at least under normal circumstances, one needs to conduct a thought experiment. Imagine that you are on but there is no air and atmosphere on it. We need to get rid of the air so we can make our model as simple as possible. Now, you will have to mentally climb to the top of a high mountain with a gun to understand why the satellites do not fall to Earth.

Let's set up an experiment

We direct the barrel of the gun exactly horizontally and shoot towards the western horizon. The projectile will fly out of the muzzle at great speed and head west. As soon as the projectile leaves the barrel, it will begin to approach the surface of the planet.

As the cannon ball moves rapidly west, it will fall to the ground some distance from the top of the mountain. If we continue to increase the power of the cannon, the projectile will hit the ground much farther from the shot. Since our planet is spherical, each time a bullet is fired from a muzzle, it will fall further because the planet also continues to rotate on its axis. This is why satellites do not fall to Earth under the influence of gravity.

Since this is a thought experiment, we can make the shot of the gun more powerful. After all, we can imagine a situation in which the projectile is moving at the same speed as the planet.

At this speed, with no air resistance to slow it down, the projectile will continue to orbit the Earth forever as it continuously falls towards the planet, but the Earth will also continue to fall at the same speed, as if "eluding" the projectile. This condition is called free fall.

On practice

In real life, things are not as simple as in our thought experiment. Now we have to deal with air resistance, which causes the projectile to slow down, eventually depriving it of the speed it needs to stay in orbit and not fall to Earth.

Even at a distance of several hundred kilometers from the surface of the Earth, there is still some air resistance that acts on satellites and space stations and causes them to slow down. This drag eventually causes the spacecraft or satellite to enter the atmosphere, where it would normally burn up due to friction with the air.

If space stations and other satellites did not have the boost to push them higher in orbit, they would all fall to Earth unsuccessfully. Thus, the speed of the satellite is adjusted so that it falls on the planet at the same speed with which the planet curves away from the satellite. That's why satellites don't fall to Earth.

Planet interaction

The same process applies to our Moon, which is moving in a free-fall orbit around the Earth. Every second, the Moon is approaching about 0.125 cm to the Earth, but at the same time, the surface of our spherical planet is moving the same distance, evading the Moon, so they remain in their orbits relative to each other.

There is nothing magical about orbits and the phenomenon of free fall - they only explain why satellites do not fall to Earth. It's just gravity and speed. But it is incredibly interesting, however, like everything else related to space.

There are over 1,000 artificial satellites in orbit around the Earth right now. They perform a variety of tasks and have a different design. But one thing unites them - the satellites revolve around the planet and do not fall.

Quick explanation

In fact, satellites are constantly falling to Earth due to the effects of gravity. But they always miss, because they have a lateral speed set by inertia at launch.

The rotation of the satellite around the Earth is its constant fall past.

Extended explanation

If you throw the ball into the air, the ball comes back down. It's because of gravity- the same force that keeps us on Earth and does not allow us to fly into outer space.

Satellites get into orbit thanks to rockets. The rocket must take off up to 29,000 km/h! This is fast enough to overcome the strong gravity and leave the Earth's atmosphere. As soon as the rocket reaches the desired point above the Earth, it releases the satellite.

The satellite uses the energy received from the rocket to stay in motion. This movement is called momentum.

But how does a satellite stay in orbit? Wouldn't it fly in a straight line into space?

Not really. Even when a satellite is thousands of miles away, Earth's gravity still pulls it. The gravity of the Earth, combined with the momentum from the rocket, causes the satellite to follow a circular path around the Earth - orbit.

When a satellite is in orbit, it has a perfect balance between momentum and Earth's gravity. But finding this balance is quite difficult.

Gravity is stronger the closer an object is to the Earth. And the satellites that orbit the earth have to travel at very high speeds to stay in orbit.

For example, the NOAA-20 satellite orbits only a few hundred kilometers above the Earth. It must travel at 27,300 km/h to stay in orbit.

On the other hand, the NOAA GOES-East satellite orbits the Earth at an altitude of 35,405 km. To overcome gravity and stay in orbit, it needs a speed of about 10,780 km/h.

The ISS is at an altitude of 400 km, so its speed is 27,720 km/h

Satellites can stay in orbit for hundreds of years, so we don't have to worry about them falling to Earth.

The Earth has more than a thousand working satellites. And if we do not pupate in our development, their number by the end of the century can grow by an order of magnitude. Despite this, the very reason for their relatively successful functioning, as it turned out, is not entirely clear. Yes, yes, actually they should fall.

Imagine a spherical Earth in a vacuum. In this case, the orbits of the satellites are not affected by disturbing factors, and they can remain there, above our heads, almost forever.

If the Earth were as round as in the picture, the Moon's gravity would knock any satellite out of orbit in a matter of months without powerful vernier engines. (Shutterstock illustration.)

The real Earth also lives in a vacuum, but it is not strictly spherical. In addition, she has the Moon - a body that, with its gravity, introduces the main disorder into the unfriendly family of circumplanetary satellites and space debris. The frontal application of the laws of celestial mechanics to the influence of the Moon on artificial objects in space leads to the conclusion that it must in a short time lead to the fall of such bodies into the earth's atmosphere with their subsequent combustion.

If you have instinctively looked at your navigator to make sure that the GPS / GLONASS satellites have not yet fallen on your head, then we understand you. The situation looks a little puzzling. What kind of saving force keeps all these tons of iron in height?

The notorious Scott Tremaine and Tomer Yavetz from Princeton University (USA) became seriously interested in this issue and tried to find out with the help of computer simulation what prevents satellites from crashing into the Earth. According to calculations, the aforementioned “non-sphericity” of our planet, as well as the influence of the Sun, are to blame for this.

Our planet, if you remember, is slightly flattened at the poles and slightly convex along the equator, which is a natural result of its rotation. And this very equatorial "influx" creates such an addition to the Earth's gravity, calculated for the sphere, that any effect of the Moon or other large objects is compensated and one or another satellite cannot quickly move in one direction, usually having several years in orbit .

Moreover, if there were no gravitational influence of the Sun, then this alone would not be enough to compensate for the influence of the Moon. And only these swan, crayfish and pike keep the cart of near-Earth spacecraft in place, preventing it from sliding into the ravine of the earth's atmosphere.


Shutterstock illustration.

It is interesting that the calculations clearly show that if our planet were slightly closer to the sphere, the satellites would inevitably and relatively quickly deorbit. On the one hand, this, of course, would save us from some of the space debris. On the other hand, what is the use of a tow truck that hunts for all the cars on the road, and not just for carelessly parked ones?

Adapted from NewScientist. The splash screen image belongs to Shutterstock.

As you know, geostationary satellites hang motionless above the earth over the same point. Why don't they fall? Is there no gravity at that height?

Answer

A geostationary artificial Earth satellite is an apparatus that moves around the planet in an easterly direction (in the same direction as the Earth itself rotates), in a circular equatorial orbit with a period of revolution equal to the period of the Earth's own rotation.

Thus, if we look from the Earth at a geostationary satellite, we will see it hanging motionless in the same place. Because of this immobility and the high altitude of about 36,000 km, from which almost half of the Earth's surface is visible, relay satellites for television, radio and communications are placed into geostationary orbit.

From the fact that a geostationary satellite constantly hangs over the same point on the Earth's surface, some people make the wrong conclusion that the force of attraction to the Earth does not act on the geostationary satellite, that the force of gravity disappears at a certain distance from the Earth, i.e. they refute the very Newton. Of course it is not. The very launch of satellites into geostationary orbit is calculated precisely according to Newton's law of universal gravitation.

Geostationary satellites, like all other satellites, actually fall to the Earth, but do not reach its surface. They are affected by the force of attraction to the Earth (gravitational force), directed towards its center, and in the opposite direction, the satellite is affected by the centrifugal force repelling from the Earth (inertia force), which balance each other - the satellite does not fly away from the Earth and does not fall on it exactly just like a bucket spinning on a rope remains in its orbit.

If the satellite did not move at all, then it would fall to the Earth under the influence of attraction to it, but satellites move, including geostationary ones (geostationary ones - with an angular velocity equal to the angular velocity of the Earth's rotation, i.e. one revolution per day, and for satellites of lower orbits, the angular velocity is greater, i.e., they have time to make several revolutions around the Earth in a day). The linear velocity reported to the satellite parallel to the Earth's surface during direct launch into orbit is relatively large (in low Earth orbit - 8 kilometers per second, in geostationary orbit - 3 kilometers per second). If there were no Earth, then the satellite would fly in a straight line at such a speed, but the presence of the Earth makes the satellite fall on it under the influence of gravity, bending the trajectory towards the Earth, but the surface of the Earth is not flat, it is curved. As far as the satellite approaches the surface of the Earth, so much the surface of the Earth goes from under the satellite and, thus, the satellite is constantly at the same height, moving along a closed trajectory. The satellite is falling all the time, but it can never fall.

So, all artificial satellites of the Earth fall to the Earth, but - along a closed trajectory. Satellites are in a state of weightlessness, like all falling bodies (if the elevator in a skyscraper breaks down and starts to fall freely, then the people inside will also be in a state of weightlessness). Astronauts inside the ISS are in weightlessness not because the force of attraction to the Earth does not act in orbit (it is almost the same there as on the surface of the Earth), but because the ISS falls freely to Earth - along a closed circular trajectory.