• The occupants of the International Space Station (ISS) "float" because the movement of the latter cancels out Earth's gravity, according to our partner The Conversation.

  • The human brain has to get used to this situation so sometimes astronauts feel like throwing up at the start of their stay in space (but after a few days it gets a lot better).

  • The analysis of this phenomenon was carried out by Valentine Bouet, teacher-researcher in Biology, Neurosciences and Pharmacology at the University of Caen Normandie.

It is true that it seems magical to be able to fly like astronauts do, being very light, without constraints, without weight… Well no!

It is not magic and physics allows to understand this perfectly.

Imagine that you throw a stone far in front of you… It will fall far from you.

If you throw it very, very, very hard, it will fall very, very, very far.

If you launch it with a catapult powerful enough so that it does not fall back, it will start to circle the earth, it is said to be "in orbit".

It's a bit as if your pebble was on one side thrown away from the earth thanks to the speed you gave it at the time of the throw but that it was also attracted by the Earth (because the Earth has a mass important therefore attracts objects).

An object launched strong enough to be put into orbit will always rotate at the same distance from the earth © Brandir / Vikidia CC BY-SA 2.5

The projection of your throw and the attraction of the Earth put it in an intermediate position, in orbit around the earth, that is to say that it will turn almost always at the same distance from the earth.

When earth's gravity disappears

When you're in space, like in the international space station where Thomas Pesquet and his teammates are now, you're like your stone locked in a big box in orbit.

It is a kind of permanent free fall, that is to say that it is as if the station fell towards the Earth which attracts it, while being propelled very far since it was launched with a very large speed.

The space station is driven by its speed (it moves at a speed of 28,000 km / h, which allows it to circle the earth in about 1 hour 30 minutes).

And in this configuration, we no longer feel the effects of terrestrial gravity and therefore we no longer have any weight and we float.

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"What is weightlessness?"

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When our body is in zero gravity (we also say weightlessness), even if it seems that everything is very simple, it is not really the case.

Our brain, used to gravity, loses a large number of landmarks when we are in zero gravity.

Indeed, on Earth, our brain is constantly informed about what is happening inside and outside our body.

When the body finds itself in zero gravity, it is therefore a little helpless ...

But what exactly is he missing?

Already, she is missing most of the information she usually receives from the vestibular apparatus, which is a small organ located in the inner ear (behind the eardrum).

This organ allows the brain to constantly know the position and movements of the head and its position.

For example, it allows the brain to know where the top and bottom are.

Thomas Pesquet “floating” on a spacewalk © NASA / Flickr CC BY-SA 2.0

Be careful not to throw up in your suit!

It may seem unnecessary but it is nevertheless essential to stand up, to find one's way in space, to adapt the movements of our eyes when our head moves, etc.

In weightlessness, this information is absent or erroneous so there is no more up or down and when you move your head, the message sent to the brain is distorted to say the least.

It's the kind of thing that can already make you want to throw up, a bit like when you're on a merry-go-round that goes all over the place very quickly.

Astronauts sometimes feel nauseous and want to vomit at the start of their stay (we call it space sickness, a bit like seasickness, then they adapt and after a few days it gets much better).

Our “Thomas Pesquet” dossier

There are also many other changes that are going to take place in the body due to weightlessness.

The muscles for example, especially those which are used a lot on earth to fight against gravity like those of the legs for example, will be so little used that they will “melt”, become smaller and less powerful.

Astronauts need to get plenty of exercise to prevent this, at least 2 hours a day!

Fortunately, despite all of this our body continues to function more or less normally and astronauts always say that they really like this fantastic sensation of floating, and we all dream of trying!

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This analysis was written by Valentine Bouet, teacher-researcher in Biology, Neurosciences and Pharmacology at the University of Caen Normandie.


The original article was published on The Conversation website.

Declaration of interests

Valentine Bouet does not work, do not advise, do not own shares, do not receive funds from any organization that could benefit from this article, and has not declared any affiliation other than her research organization.

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