There is no gravity in space
Gravity exists throughout space and never reaches zero. Astronauts on the International Space Station experience about 90 percent of Earth's surface gravity, but they appear weightless because the station and its crew are in continuous free fall around Earth, which is the definition of orbital flight.
What we know
Gravity is a universal force that diminishes with distance but never completely disappears. At the altitude of the ISS, roughly 400 km above Earth's surface, gravitational acceleration is still about 8.8 m/s squared compared to 9.8 m/s squared at sea level. This is why the term microgravity, meaning very small but nonzero gravity, is more accurate than zero gravity.
NASA explains that astronauts float aboard the ISS not because they are outside gravity's reach but because they are in free fall. The station is moving horizontally at approximately 28,000 km/h, so fast that as it falls toward Earth, the curvature of Earth curves away beneath it at the same rate. The station is constantly falling toward Earth but continuously missing it, which is what an orbit is.
Everything inside the falling station, including the astronauts, falls together at the same rate. Because there is no relative motion between them and the spacecraft due to the fall, they experience no contact forces and appear to float. This is the same principle as the momentary weightlessness felt inside an elevator in free fall.
Gravity also shapes all large-scale structures in the universe: galaxies, stars, and planetary orbits all exist because of gravitational attraction. The Moon remains in orbit around Earth, and Earth around the Sun, because of gravity at cosmological distances.
Common claims
- Astronauts float because there is no gravityFalse - they are in free fall
- There is zero gravity in outer spaceFalse - gravity exists everywhere, diminishing with distance
- The ISS is outside Earth's gravitational fieldFalse - ISS experiences roughly 90% of surface gravity