At what altitude does weightlessness begin?

How high you need to go, if at all, to experience microgravity...
27 July 2021


this is a picture of an astronaut doing a space walk



Listener Wolfgang is wondering...

"How many kilometres from the Earth's surface does weightlessness begin?"


Space science junkie and journalist Richard Hollingham didn't get weighed down answering this question:

Richard - Well, as you move away from any object, gravity is going to decrease. If you were in deep space, for example, away from any planets and away from any black holes, stars, anything that would have a lot of gravity, then you would be weightless. You would be able to float around. On the International Space Station, there is only about 90% of the gravity on Earth. So there's actually something else going on here, what they call microgravity in space. And actually if you were on the International Space Station or on one of these parabolic flights, the astronauts are in free fall. So with a parabolic flight, you're going up, over, round, out of the atmosphere and back down again. In that period at the top of the parabola, you've got weightlessness. You're falling back down to Earth. You've got the weightlessness. It's like going on a rollercoaster. But with the International Space Station, what's happening there is you're falling around the Earth. So it's because the space station is going so fast but it's going to hit the ground.

Chris - And therefore it's not so much about the altitude. It's more about how long you're falling for. So when you've got these craft climbing up, such as Wally Funk would have experienced, when we recorded this programme today, she would have gone up, gone over the top of the rollercoaster, as it were and started to come down. The higher she went, the longer she would have had to fall for and therefore experience weightlessness. But if she'd gone to a less high height, she could still have felt weightless. It just wouldn't have lasted so long.

Richard - Yeah. absolutely. And with that flight, you had about four minutes of weightlessness.


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