Astronauts float in space because they are in a state of microgravity. In reality, they are not floating, but are in a constant free fall around the Earth, which gives the impression of floating.
When an object like a space station orbits the Earth, it is actually in constant free fall. In simple terms, it is continuously falling toward our planet, pulled by Earth's gravity. But it is also moving forward very quickly, so fast that its curved trajectory naturally follows the shape of the Earth. The result: it falls without ever hitting the ground, it circles around. Inside, astronauts fall at exactly the same rate as their spacecraft, so they float in a feeling of weightlessness. It's a bit like when you drop very quickly on a roller coaster or in a fast elevator, except up there, this sensation lasts all the time.
Microgravity is when you experience an extremely low, almost nonexistent weight, but it's not zero. It's different from the total absence of gravity, which practically doesn't exist anywhere in space. In fact, astronauts float because they are in a constant free fall around the Earth. They are constantly falling towards it, and since their entire environment is falling at the same rate, they no longer feel their own weight. This particular situation of continuous free fall gives you the impression that gravity has almost disappeared: we call this microgravity.
To float in a space station, astronauts must move at a very high orbital speed, about 28,000 km/h. At this speed, their trajectory constantly follows the curvature of the Earth. In other words, they are falling toward the ground, but moving so fast that they continually "miss" our planet. This perpetual free fall around the Earth keeps them in a state of weightlessness. Without this precise speed, it would be impossible to remain in orbit: they would either crash or drift into space.
Contrary to popular belief, if an astronaut floats in their capsule, it is not because they are far from Earth. Even at an altitude of 400 km (like in the International Space Station), Earth's gravity remains strong, at about 90% of that at ground level. What really changes as you move away is that the speed needed to stay in orbit decreases as the distance increases. The farther you go from Earth, the less speed you need to avoid falling back. The sensation of floating therefore does not come from a lack of gravity, but simply from being in a continuous free fall around our planet.
At first, astronauts' bodies are completely disoriented by weightlessness. In orbit, the brain doesn't know where is up and where is down, often causing nausea or dizziness for a few days. Fortunately, our body is clever and eventually adapts to this new reality: the brain quickly relearns to determine its orientation differently. Muscles rapidly lose strength, so astronauts engage in daily workouts on specialized treadmills or by using resistance bands. Bones also become more fragile, as they no longer support any weight: to counter this, they regularly perform specific exercises. Little by little, the body regains a semblance of balance in this strange environment where everything floats.
In microgravity, astronauts sometimes temporarily grow a few centimeters because their spine relaxes when it is no longer subjected to the weight of their body and Earth's gravity.
Contrary to popular belief, astronauts float not because there is no gravity, but because they are in a state of perpetual free fall around the Earth, following an orbital trajectory.
Microgravity doesn't just affect humans: even flames burn differently in space. They take on the shape of small blue spheres due to the lack of convection, which directly impacts heat diffusion and oxygen supply.
Did you know that the sensation of weightlessness can temporarily disrupt astronauts' spatial orientation? That's why they train intensively in a pool, simulating microgravity before going to space.
In microgravity, astronauts' spines elongate slightly because gravity no longer compresses their intervertebral discs as much. Thus, an astronaut can temporarily gain a few centimeters in height during their time in space, but this height returns to normal as soon as they come back to Earth.
To sleep comfortably, astronauts use sleeping bags attached to the walls of the space station to avoid drifting freely during their sleep. Some even prefer to lightly strap themselves in to regain the reassuring sensation of having a solid support.
Technically, yes, it would be possible to recreate artificial gravity using the centrifugal force generated by the rotation of part or all of the space shuttle. However, to date, this process has not been implemented on space stations due to technical difficulties, costs, and practical considerations.
Over long periods, microgravity indeed affects the human body. The loss of muscle and bone mass, cardiovascular changes, and alterations in the immune system are caused by prolonged absence of gravity. That is why astronauts follow a daily routine of rigorous physical exercises.
The term "weightlessness" might wrongly suggest a total absence of gravity. However, even in orbit, astronauts experience a slight gravitational force known as microgravity. They float because they are in a continuous free fall around the Earth.
No one has answered this quiz yet, be the first!' :-)
Question 1/5
