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 a device that moves around the planet in an easterly direction (in the same direction as the Earth itself rotates), along 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). The 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 the Earth - along a closed circular trajectory.

Why doesn't the satellite fall to Earth?

This question is often heard. A qualitative answer to it can be obtained with the help of the following mental experiment. Let's assume that there is a mountain on Earth 200 km high and you have climbed to its top. Throw a rock from the top of a mountain. The more you swing, the further the stone will fly. At first, it will fall on the side of the mountain, then at its sole, and, finally, the point of its fall will be hidden somewhere beyond the horizon. Of course, we assume that you have a truly Herculean power (which, of course, helped a lot with clean mountain air). You can throw a stone in such a way that it will fall on the opposite side of the Earth and even at the foot of the mountain, but on the other hand, circled the Earth. A little more effort and the stone, circled the Earth, will whistle over your head, turning into a kind of boomerang. And now now connect the flight of the stone with the question - why does the satellite not fall to the Earth.

The above thought experiment shows that the satellite is constantly falling to the Earth. Do not be surprised, it falls and tries to touch the surface of the Earth. What's the matter? Let's assume that the Earth has the shape of a sphere, its field is central and the flight of satellites occurs directly above its surface, say, at a height of one meter. Theoretically, this is possible. On fig. 21 through OA the radius of the circular orbit of the satellite is indicated. Let at some moment the satellite be at point A and the speed of its flight is directed along the line AB, perpendicular to the radius OA.

If there were no attraction of the Earth, then after some short time the satellite would be at point B, which lies on the continuation of the velocity vector, and would move away from point A at a distance AB. But due to the attraction of the Earth, its flight path is curved and therefore the satellite will end up at some point C. And this means that when we consider the flight of a satellite at a constant speed with a simultaneous “fall” towards the Earth due to its attraction, we get nothing more than Roundabout Circulation. Now it becomes clear why the satellite does not reach the Earth's surface: how much the satellite deviates from rectilinear motion due to the influence of the Earth's gravity forces, to the extent that the Earth's surface due to sphericity "departs" from a straight line. Figuratively speaking, the satellite is constantly trying, as it were, to reach the surface of the Earth, and the surface of the Earth, curving, runs away from it. And this process continues throughout the flight, as a result of which the satellite cannot reach the Earth's surface in any way. However, the paradoxical nature of this phenomenon is not surprising, it can be found a decent "earthly" analogy. Recall the experience when the rotation of a weight on an extended string was considered. In the process of rotation, you are constantly pulling the weight towards you with the help of a rope, but nevertheless it never reaches your hand and this does not surprise you at all. Something similar happens on a cosmic scale: the force of gravity of the Earth is the very rope that holds the satellite and makes it rotate around the Earth.

The Earth has a powerful gravitational field, which attracts not only objects located on its surface, but also those space objects that, for some reason, are in close proximity to it. But if this is so, then how to explain the fact that artificial satellites launched by man into the earth's orbit do not fall on its surface?

According to the laws of physics, any object in the earth's orbit must necessarily fall on its surface, being attracted by its gravitational field. All this is absolutely true, but only if the planet had the shape of an ideal sphere, and external forces would not act on objects in its orbit. In fact, it is not. The earth, due to rotation around its own axis, is somewhat swollen at the equator, and flattened at the poles. In addition, artificial satellites are affected by external forces emanating from the Sun and the Moon. For this reason, they do not fall to the surface of the Earth.

They are kept in orbit precisely due to the fact that our planet is not ideal in shape. The gravitational field emanating from the Earth tends to attract satellites, preventing the Moon and the Sun from doing the same. There is a compensation of the gravitational forces acting on the satellites, as a result of which the parameters of their orbits do not change. During their approach to the poles, the earth's gravity becomes less, and the moon's gravitational force is greater. The satellite begins to move towards her. During its passage through the equatorial zone, the situation becomes directly opposite.

There is a sort of natural correction of the orbit of artificial satellites. For this reason, they do not fall. In addition, under the influence of the earth's gravity, the satellite will fly in a rounded orbit, trying to get closer to the earth's surface. But since the Earth is round, this surface will constantly run away from it.

This fact can be demonstrated with a simple example. If you tie a weight to a rope and start rotating it in a circle, then it will constantly strive to run away from you, but cannot do this, held by the rope, which, in relation to satellites, is an analogue of earth's gravity. It is she who keeps satellites in their orbit, striving to fly into outer space. For this reason, they will forever revolve around the planet. Although, this is purely a theory. There are a huge number of additional factors that can change this situation and cause the satellite to fall to Earth. For this reason, orbit correction is constantly being carried out on the same ISS.

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.

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.