Videos of astronauts floating inside a spacecraft can make space look like a place without gravity. Yet gravity is exactly what keeps a spacecraft in orbit around Earth. The apparent contradiction disappears when the spacecraft’s motion is considered. [1]
Gravity reaches into orbit
Earth’s gravitational pull becomes weaker with distance, but it does not suddenly end at the top of the atmosphere. At the approximate altitude of the International Space Station, gravity remains about 90 percent as strong as it is at Earth’s surface. [1]
The station, its crew, and the objects inside it are all being pulled toward Earth. A floating tool is not escaping gravity. It is sharing the motion of the spacecraft surrounding it. [1]
Falling without hitting the ground
An orbiting spacecraft also travels sideways at high speed. While gravity bends its path toward Earth, the curved surface of Earth falls away beneath that path. With the right motion, the spacecraft keeps missing the ground: it is continuously falling around the planet. [2]
This is why orbit is different from simply hovering far above a location. The sideways movement and the inward gravitational pull work together to produce a curved trajectory. [2]
Everything falls together
Inside the station, astronauts and loose objects fall along with their surroundings. There is no usual floor pushing upward against their feet. Relative to the cabin, they can drift rather than stand with the familiar sensation of weight. [2]
What microgravity means
This environment is commonly called microgravity. It describes conditions in which objects appear nearly weightless, not a region where gravity has vanished. Small disturbances prevent real spacecraft from being perfectly weightless environments. [1]
So the next floating object in a space video offers a clue to the larger scene. The object, astronaut, and spacecraft are traveling together through a gravitational field. Floating is evidence of their shared fall. [2]
Sources and image credit
1. NASA: What Is Microgravity? — Grades 5–8
2. NASA Glenn Research Center: What Is Microgravity?
Cover: NASA / Apollo 17 crew. Public domain. Resized and cropped or letterboxed to a 16:9 cover. Image source · Usage / license