Why do astronauts float in space?

Astronauts float in space because they and the spacecraft in which they are traveling are orbiting the Earth in a free-fall trajectory that matches the curvature of the planet. By free falling around the Earth, the astronauts and their spacecraft avoid burning up in the atmosphere.

Between 200 and 250 miles, the typical orbit height of the International Space Station, the force of Earth's gravity pulling on the station and its occupants while in orbit is still about 90 percent of that found on the planet's surface. Astronauts appear to float inside the space station because the station and its occupants are falling around the Earth at the same rate.