Astronauts and Weightlessness

What is Weightlessness?

To be really ‘weightless’ you must be at a place in the universe where there is no gravity at all. But we have just said that satellites are kept in orbit by the pull of gravity (in fact the astronauts in a space shuttle which orbits at a distance of 320 kilometres above the Earth still weigh about 90% of what they do on the ground – that means that Earth’s gravity is 90% as strong as it is on the ground).

Why then do we see pictures of astronauts bouncing around ‘weightless’ inside their spacecraft?

This is not because there is no gravity there, but because both the spacecraft and the astronauts are both moving together under the influence of gravity.

Have you ever been in a lift which suddenly goes down very quickly? Or have you ever been in a plane which goes down very suddenly and quickly when it gets into an ‘air pocket’ of low pressure? Or been on a roller-coaster or Big Wheel that suddenly goes down? Can you remember what it feels like?

This is called ‘freefall’ or ‘weightlessness’. This is the feeling you have when you and the object you are in are both falling together.

This can create some problems however!

Although some things are easier in weightless conditions, many things are harder. Most importantly, because things are ‘weightless’ with nothing holding them down, nothing stays put. Liquids, foods, tools and even sleeping people, all have to be carefully managed, contained, or strapped down to keep them from drifting away.

Effects of Weightlessness on the Human Body

Being weightless in space looks like fun, but how do you think it might affect the human body?

Our bodies are designed to function under the force of gravity. Astronauts’ muscles get smaller and their bones get weaker because they do not have to support the full body weight. The fluids in the body are affected too and some astronauts often complain of blocked sinuses and congestion. So spending too long in a weightless environment can damage your health.

Sometimes a kind of artificial gravity is created by having a specially-shaped spinning spacecraft that makes the astronaut feel a push upwards from the ‘floor’.

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