We think of astronauts as floating in zero gravity, but the International Space Station is still deep inside Earth’s pull, where gravity is nearly 90% as strong as it is on the ground. What looks like weightlessness is really the station and its crew falling around the planet at about 28,000 kilometres per hour.

We think of astronauts as floating in zero gravity, but the International Space Station is still deep inside Earth’s pull, where gravity is nearly 90% as strong as it is on the ground. What looks like weightlessness is really the station and its crew falling around the planet at about 28,000 kilometres per hour.

We tend to picture astronauts drifting weightlessly in “zero gravity,” as if the pull of the Earth simply stops a few hundred kilometres up. It does not. The International Space Station orbits deep inside Earth’s gravity, at an altitude where the pull is still nearly 90 per cent as strong as it is on the ground. What looks like weightlessness is something else entirely: the station and everyone aboard it are falling around the planet at about 28…