What happens to gravity in space?

Gravity falls off with the square of the distance from the centre of the body producing it. At 400 km altitude, where the International Space Station flies, it is still around 90% of the value at the surface. In geostationary orbit, almost 36,000 km higher, it is already about forty times weaker, and at the Moon's distance it becomes tiny, though still enough to have kept our satellite circling for billions of years.

An astronaut in orbit is not beyond gravity's reach: they are falling with it. Spacecraft and occupants descend with the same acceleration while moving at about 28,000 km/h, so no surface pushes against another and weight, which is precisely that contact force, is cancelled out. The technical name is microgravity, because vibrations, atmospheric drag and the crew's own movements leave residual accelerations.

Without weight, liquids gather into spheres and stick to whatever they touch; hot air does not rise, so a flame forms a bluish bubble and goes out if there is no ventilation; and exhaled carbon dioxide lingers around the face unless a fan sweeps it away. Body fluids shift toward the head, which swells the face, congests the nose and presses on the optic nerve.

There are also places where pulls balance out. At the Lagrange points of the Earth-Sun system, gravitational forces and orbital motion cancel out enough for a spacecraft to stay in place while spending almost no propellant: there, about 1.5 million kilometres from Earth, the James Webb telescope operates. That, too, is not an absence of gravity, but gravity in balance.