Why does the station stay in space and not return to Earth?

It has been a month since Thomas Pesquet joined the International Space Station on his second visit, which will last for six months.
The challenge of living in space is formidable and begins with a simple question: Why does the station stay in space and return to Earth, like rocket pieces that bring in its inhabitants?

This question can be taken in the opposite direction: Why do we stay on Earth? Why is it difficult to stay away from it? And it is that the earth exerts a force that permanently draws us to it. This attraction is called gravity. It is a law of physics that is easy to express: any object that has mass attracts other bodies to it. The heavier the objects, the more they are attracted to each other; On the other hand, the farther away, the less attractive it is.

Thus, the Earth’s gravitational pull on the space station, which lies between 330 and 420 kilometers above sea level, is weaker than that exerted on us who walk on its surface.

But there is one more thing: the space station is moving very fast, at more than seven kilometers per second. This displacement tends to move it away from the Earth and thus creates an opposing force of gravity. Ultimately, therefore, the space station remains close to Earth.

The force of gravity allows us to understand a lot of things about the universe. This depends, as we have seen, on the masses of the two bodies. Thus the Earth’s gravity to the Moon is sufficient to keep the Moon around the Earth even though it is very far away. Likewise, this is what sustains the particles of the air we breathe, creating the atmosphere and enabling life on Earth. Finally, it is she who keeps Earth and all other planets at a certain distance from the sun.

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Finally, if this law seems simple to express and explain a lot of things, then it is interesting to say that its operation has not yet been fully explained: How does the Earth, which is located millions of kilometers from the Sun, feel its gravity? This is one of the challenges facing scholars of the twenty-first century, perhaps one hacked by a reader of Actuailes!

So the next time you look at satellites or stars in the sky, you can marvel at the beauty of the world we live in, and wonder what is really going on behind these forces, while you continue to live calmly: there is no danger of them falling out. Us tomorrow!

Malo de Preto

Acts No. 132 – May 26, 2021

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