The Earth has a powerful gravitational field that attracts not only objects located on its surface, but also those space objects that, for some reason, find themselves 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 located in the earth's orbit must fall onto 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 no external forces acted on objects located in its orbit. In fact, this is not so. The Earth, due to its rotation around its own axis, is somewhat inflated at the equator and flattened at the poles. In addition, artificial satellites are affected by external forces emanating from the Sun and Moon. For this reason, they do not fall to the surface of the Earth.

They are kept in orbit precisely because our planet is not ideal in shape. The gravitational field emanating from the Earth tends to attract satellites to itself, preventing the Moon and Sun from doing the same. The gravitational forces acting on the satellites are compensated, as a result of which the parameters of their orbits do not change. As they approach the poles, the Earth's gravity becomes less, and the gravitational force of the Moon becomes greater. The satellite begins to shift in her direction. During its passage through the equator zone, the situation becomes exactly the opposite.

There is a kind of natural correction of the orbit of artificial satellites. For this reason they do not fall. In addition, under the influence of 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 by simple example. If you tie a weight to a rope and start rotating it in a circle, then it will constantly try 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 holds satellites in their orbit that are trying 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 carried out on the same ISS.

Right now there are more than 1,000 artificial satellites in Earth's orbit. They perform a wide variety of tasks and have different designs. But they have one thing in common - the satellites revolve around the planet and do not fall.

Quick explanation

In fact, satellites fall to Earth all the time due to gravity. But they always miss, because they have a lateral speed set by the inertia at launch.

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

Explanation

If you throw a ball in the air, the ball comes back down. This is because gravity- the same force that keeps us on Earth and prevents us from flying into outer space.

Satellites are launched into orbit by rockets. The rocket must accelerate up to 29,000 km/h! This is fast enough to overcome the strong gravity and escape the Earth's atmosphere. Once 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 impulse.

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

Not really. Even when the satellite is thousands of kilometers away, Earth's gravity still pulls on it. The Earth's gravity, 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 perfect balance between momentum and the force of gravity of the Earth. But finding this balance is quite difficult.

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

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

On the other hand, NOAA's 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 located 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.

Illustration copyright Getty Images

The amount of space debris in low-Earth orbit is steadily growing. The columnist decided to figure out what happens when spent satellites fall to Earth. German scientists are studying this problem.

The building in which Willems is going to show me “the most interesting things” belongs to the institute for aerodynamic research of the German Aviation and Space Center (DLR), located in Cologne.

Willems also lists the wind tunnel control center with a huge old remote control, which has many sensors, switches and buttons, as “not the most interesting”.

Passing a massive blast-proof door, we enter a windowless room. The walls are covered with soot, and the smell of gunpowder is clearly felt in the air.

Aerodynamic tests of rocket engines are carried out here.

But this, as it turns out, is not the most interesting.

Willems performs his “most interesting” experiments in one of the wind tunnels of the Cologne center. It simulates the departure of a satellite from Earth orbit.

“There are a huge number of artificial satellites now circling the Earth, and all of them will sooner or later leave orbit,” explains Willems.

Could satellite debris that didn't burn up in the atmosphere fall on something - or someone?

"When spacecraft enter the atmosphere, they are destroyed. We are interested in what is the likelihood that their fragments will survive."

In other words, could debris from spent satellites that did not burn up in the atmosphere fall on something - or someone - on Earth?

The wind tunnel installed on a concrete floor, which was allocated for Willems’ experiments, resembles a huge, half-disassembled vacuum cleaner connected to a steamer.

The shiny unit is covered in a network of pipes and electrical wires. Typically, this pipe is used to blow through models of supersonic and hypersonic aircraft - the speed of the air flow created in it can exceed the speed of sound by 11 times.

More and more satellites will fall from the sky

The “pipe” itself is a spherical metal chamber two meters high, inside which models for purging are secured in special clamps.

But Willems doesn't need clamps - he simply throws objects into a pipe through which air flows in the opposite direction at a speed of about 3000 km/h (which is twice the speed of sound).

Illustration copyright Getty Images Image caption As a rule, satellites are destroyed upon entry into the atmosphere.

In this way, the flight of a satellite deorbiting through the earth's atmosphere is simulated.

“We put objects in air flow to see how they behave in simulated free fall,” says Willems.

"The duration of each experiment is only 0.2 seconds, but this is enough time to take many pictures and the necessary measurements."

The data obtained during the experiments will be entered into computer models, thanks to which it will be possible to more accurately predict the behavior of spacecraft when leaving orbit. ( In this video DLR the destruction of the Rosat satellite in the earth's atmosphere was simulated.)

There are currently some 500,000 pieces of orbital debris orbiting the Earth, ranging from small metal fragments to entire spacecraft the size of buses, such as the European Space Agency's Envisat satellite, which abruptly stopped operating in April 2012.

"Overall, the number of pieces of debris whose trajectories we're tracking is growing," says Huw Lewis, senior lecturer in aircraft and rocket science at Britain's University of Southampton.

As the volume of orbital debris grows, the likelihood of collisions with operating satellites or manned spacecraft will also increase.

The problem of orbital debris will remain relevant for a long time

Already now, for this reason, the orbit of the International Space Station has to be periodically adjusted.

"Fragments of spent vehicles have been de-orbiting since the beginning of space exploration," Lewis said. "Typically, a large object enters the atmosphere once every three to four days, and this problem will remain relevant for a long time."

Although satellites in the atmosphere are destroyed by overloads and high temperatures, some large debris falls to Earth relatively intact.

"For example, fuel tanks," says Lewis. "Some spacecraft have them the size of a small car."

Illustration copyright Getty Images Image caption Most spent satellites are deorbited so that they disintegrate in the atmosphere over uninhabited ocean areas.

Although Willems does not throw cars into a wind tunnel, his goal is to see how large objects behave when destroyed, and which of their fragments could theoretically reach the earth's surface.

“The flow around one component affects the flow around its neighbors,” he explains. “Depending on whether they fall to the Earth individually or as a group, the degree of probability of their complete combustion in the atmosphere also changes.”

But if space debris leaves orbit so often, why doesn’t its debris break through the roofs of houses and fall on our heads?

In most cases, the answer is that spent satellites are purposefully deorbited using residual onboard fuel.

The likelihood that a piece of satellite will fall on you is extremely low

In this case, the descent trajectories are calculated in such a way that the satellites burn up in the atmosphere over uninhabited areas of the oceans.

But unplanned deorbits pose a much greater danger.

One of the latest such cases was the unplanned deorbit of the Upper Atmosphere Research Satellite (UARS) of the American space agency NASA in 2011.

Despite the fact that 70% of the Earth is covered by oceans and large areas of land are still sparsely populated, the probability that the fall of UARS would lead to destruction on Earth was, according to NASA estimates, 1 in 2,500, Lewis notes.

"This is a very high percentage - we start to worry when the possible risk to the population is 1 in 10,000," he says.

“We are not talking about the fact that a piece of satellite will fall on you - the probability of this is negligible. What we mean is the probability that it will fall on someone in principle.”

Considering that more than a million people die in car accidents around the world every year, the likelihood of a piece of orbital debris causing significant destruction on Earth is very slim.

The more satellites are put into orbit, the more of them will leave it

And yet it is not neglected, since the country that launches spacecraft, in accordance with UN agreements, bears legal and financial responsibility for any damage caused by such activities.

For this reason, space agencies strive to minimize the risks associated with objects falling from orbit.

DLR's experiments will help scientists better understand and more closely monitor the behavior of space debris, including during unplanned deorbits.

The cost of space launches is gradually falling, and satellites are becoming more and more miniature, so their number will only increase in the coming decades.

“Humanity is increasingly using space, but the problem of orbital debris is getting worse,” says Lewis. “As more satellites are put into orbit, more will be removed from it.”

In other words, although the likelihood of being hit by spacecraft debris remains negligible, more and more satellites will fall from the sky.

No object launched into low-Earth orbit can remain there forever.

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

Why don't satellites fall to Earth?

The answer to this question is given back at 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 is difficult to comprehend. And therefore, when school knowledge erodes (there is even such a pedagogical term - “residual knowledge”), people again wonder why satellites do not fall to Earth and weightlessness arises inside the spacecraft during 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 enormous - approximately 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 obeys Newton's laws with very high accuracy. According to these laws, two interacting bodies, which are not influenced 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 gravity is exactly compensated by the force of pressure of the earth's surface on the surface of our body. At the same time, the Earth and our body are deformed, which is why we feel heaviness. If, for example, we begin to lift some kind of load, we will feel its weight through muscle tension and deformation of the body, 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 accelerated 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 gravity the body’s speed will begin to change both in magnitude and direction, and it will certainly fall to Earth. If the acceleration speed was more than 11.2 km/s, that is, the second cosmic speed, the body will fly away and never return to Earth.

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

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

This text is an introductory fragment.