The image of an astronaut floating effortlessly inside a spacecraft often leads many to believe that the environment beyond Earth is completely devoid of gravity. This fuels the misconception that orbiting spacecraft have traveled past the reach of our planet’s gravitational pull. However, the force that keeps our feet on the ground is still very much present, even hundreds of miles above the surface. This apparent weightlessness is not a sign of gravity’s absence, but rather a direct consequence of its continuous action.
Gravity Exists Far Beyond Earth
Gravity is a fundamental property of the universe; any object possessing mass exerts a pull on every other object with mass. While this attractive force weakens with distance, it extends indefinitely throughout space. Earth’s gravity does not simply switch off once a spacecraft crosses an imaginary boundary into orbit.
The International Space Station (ISS) orbits at an altitude of approximately 400 kilometers (250 miles) above Earth. At this height, the planet’s gravitational pull is still remarkably strong, retaining about 89% to 90% of the strength experienced at sea level. If an astronaut were to stand on a platform at the ISS’s altitude, they would still feel nearly the same downward force as they do on the surface. The slight reduction in gravity is solely due to the increased distance from Earth’s center.
Why Astronauts Float
The sensation of floating, or apparent weightlessness, experienced by astronauts is caused by the state of continuous freefall, not weak gravity. The International Space Station (ISS), along with everything inside it, is constantly falling toward the Earth. This condition is identical to the feeling one would have briefly during a freefall amusement park ride.
What keeps the ISS from crashing into the planet is its immense sideways speed, which is intrinsic to how orbits work. The station travels at approximately 27,000 kilometers per hour (17,000 miles per hour), moving horizontally fast enough to keep missing the Earth as it falls. As the station accelerates downward due to gravity, the planet’s surface curves away at the same rate, resulting in a perpetual fall around the globe rather than into it.
This dynamic balance between the downward pull of gravity and the forward momentum means the astronauts and the vehicle are accelerating together at the same rate. Since there is no relative motion between an astronaut and their immediate environment, they appear to float within the cabin. This condition is correctly termed microgravity, not zero gravity.
The term microgravity is used because the environment is not one of absolute zero-G. Small residual forces, such as minute atmospheric drag or tidal forces, prevent perfect weightlessness. These forces are often one-millionth the strength of the gravity on Earth’s surface.
Gravitational Influence Across the Cosmos
Gravity extends far beyond the Earth-Moon system, acting as the organizing force for the entire universe. This force dictates the structure and motion of celestial bodies on the largest scales. Planets, for instance, are held in stable, elliptical paths around the Sun because of its powerful gravitational pull.
The Sun and all the other stars in our galaxy are bound together by the collective gravitational pull of the Milky Way’s total mass. The subtle, differential pull of gravity is also responsible for the ocean tides on Earth, as the Moon’s attraction tugs on our planet. This constant, long-range force shapes the universe from orbital mechanics to the clustering of galaxies.