How much gravity is in space compared to earth?

Gravitational acceleration falls with the square of the distance from a body's centre, and orbital altitudes are small compared with planetary radii. Earth's mean radius is about 6,371 km; a station at 400 km sits some 6,771 km from the centre. The resulting acceleration is close to 8.7 m/s² against 9.81 m/s² at sea level — around 90 percent. Crews float because the whole vehicle is in free fall, not because the pull has gone.

At geostationary altitude, 35,786 km above the equator, the picture changes. Distance from the centre grows roughly sevenfold and gravity drops to something near 0.22 m/s², a little over two percent of the surface value. Even there, it is what keeps a satellite in place.

Surface gravity varies with a body's mass and radius together, which is why intuition based on size alone misleads. The Moon offers about 1.62 m/s², roughly one sixth of Earth — the reason Apollo crews adopted a loping gait. Mars gives about 3.72 m/s², close to 38 percent. Jupiter, despite being gaseous, presents about 24.8 m/s² at its cloud tops, some 2.5 times Earth's.

True absence of gravity does not exist anywhere in the observable universe, because the field of every mass extends without limit. What exists is negligible field strength: deep interstellar space, far from any star, where residual accelerations are vanishingly small. Aboard a spacecraft the practical condition is microgravity, typically around a millionth of Earth gravity, produced by drag, tidal gradients along the vehicle and the movement of the crew themselves.