What is gravity like in space?

Newton's formula shows that gravitational pull falls off with the square of the distance to Earth's center, not with altitude above the ground. Since Earth's radius is about 6,371 km, climbing to the International Space Station's 400 km altitude moves the vehicle only about 6% farther from the planet's center. The result is a gravity of roughly 8.7 m/s², compared with 9.8 m/s² at the surface: around 90%.

That value is still enough to fully govern the motion of the orbital complex. In fact, it is precisely Earth's gravity that keeps the station circling instead of flying off in a straight line.

What cancels out the sensation of weight is free fall. The station moves at about 7.66 km/s, a speed at which its curved path matches the curvature of the planet: it falls without ever reaching the ground. Since the vehicle, the air inside and the crew all fall at exactly the same rate, nothing presses against anything else, and everything appears weightless. The same effect is felt for a few seconds during the parabolic flights that agencies use for training and to test experiments.

Engineers prefer to talk about microgravity because the residual acceleration isn't zero: friction with the remaining atmosphere, engine burns to reboost the orbit, crew movement, and tidal gradients within the module itself leave accelerations on the order of a millionth of Earth's gravity. It's a tiny figure, but relevant for sensitive crystallography or fluid physics experiments, which are usually mounted in vibration-isolated racks.