Why astronauts float in orbit — Astronomy, 7–10 years
Astronauts in a spacecraft are not beyond gravity. They and their spacecraft are falling around Earth together, which makes them seem weightless.
Orbit is falling around Earth
A spacecraft in orbit is always being pulled towards Earth, but it is also moving sideways very fast. It keeps missing the ground as Earth curves away beneath it. Astronauts float because they, their tools and the spacecraft all fall together.
Why did people need to understand orbit?
To send a person or satellite around Earth, engineers had to solve two problems: falling back down and flying away. The right speed makes gravity bend the path into a loop, allowing a spacecraft to stay above Earth for a long time.
A simple orbit calculation
The International Space Station travels about 400 kilometres above Earth. Step 1: imagine dropping it straight down; gravity would pull it to Earth. Step 2: give it a sideways speed of about 28,000 kilometres per hour. Step 3: it falls while Earth curves away, so it keeps circling.
Gravity has not disappeared
It is reasonable to think astronauts float because there is no gravity in space: their feet do not press on a floor. But gravity is still pulling them; they feel weightless because the floor is falling with them instead of pushing back against their feet.
What orbits do for us
Satellites in orbit can take photographs of clouds, carry phone signals and help navigation systems find positions. They must travel at a suitable speed and height: too slow and they fall lower, too fast and they may move into a different path.
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