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Is There Really Gravity in Space?

Today, satellites and even people, circle Earth. Their motion is based on Newton’s principles from 300 years ago. Like Newton’s imaginary cannonball, these satellites orbit Earth. They do not fly off into outer space. They do not come crashing back to Earth. Their velocity matches perfectly. They literally make a continuous fall around Earth.

You have most likely seen images of astronauts floating in space. These images are difficult to forget. These images are in stark contrast to what we experience every day on Earth. At any given time, there are a few astronauts living aboard the International Space Station (ISS). It is positioned in low Earth orbit, between 330 and 435 km (205 and 270 mi) above Earth’s surface. The astronauts aboard the ISS spend many months at a time working in this environment. During their stay, they do not feel the effects of gravity. Is that because there is no gravity in space?

If gravity is still pulling down on objects in space, why do astronauts appear to float? The operative word is ‘appear’. Just like a skydiver, they are falling toward Earth. Astronauts aboard the ISS experience something called apparent weightlessness. This affect makes it feel to them like there is no gravity. The difference is that the ISS is traveling fast enough that as it falls, Earth curves away beneath it. Its velocity counters its rate of fall. As a result, it never crashes. The ISS orbits Earth using the same principal as Newton’s hypothetical cannon. In addition, our Moon’s orbit around Earth is also based on this same principle. The only caveat for objects orbiting Earth is the velocity must be fast enough. This velocity depends on the distance the object is above Earth’s surface. The farther away the object in orbit, the faster it must travel.