Page 4 - How to Fall Without Hitting the Ground Many people think that a satellite is one of those fancy, high-tech objects that revolves around the Earth, like Sputnik or the Hubble space telescope. That is partially correct, but a more precise definition of a satellite is any object that orbits or revolves around another object. For example, the Moon is a satellite of the Earth, and the Earth is a satellite of the Sun. However, going back to the Sputnik idea, we’re going to talk about how satellites close to Earth work, and how they stay in orbit. A good way to visualize exactly how a satellite’s orbit works is to use familiar examples here on Earth. In this case, picture a really tall mountain. You are standing on top of that mountain with a baseball in your hand. If you throw that ball quite slowly, what happens? The ball will quickly fall to the ground, because the gravitational force directed toward the center of the Earth will pull it down. If you increase the speed of the ball by throwing it faster and faster, the ball will travel further and for a longer time before returning. Nothing too exciting so far. However, if you somehow had the ability to throw the ball at an amazingly high speed, the ball would travel completely around the Earth and hit you in the back of the head. This idea of throwing something all around the Earth may seem ridiculous but think about it. As the ball travels through the air it falls towards the Earth yet, at the same time, it also travels outward, over the Earth. Now, the faster you throw the ball the more ground it will travel over before landing. If you could throw the ball fast enough it would travel so far over the ground that by the time it came down the ground would have curved away from it because, after all, the Earth is round. In this case, the ball would become a satellite orbiting around Earth! Satellites in LEO (Low Earth Orbit) must travel really fast so that the pull of gravity doesn’t tug them back into the atmosphere. Satellites which orbit further away from the Earth, like the moon, still behave just like our imaginary ball. Basically, the object is traveling fast enough that as it is pulled towards the Earth, it avoids hitting the Earth because of its speed. That is how a satellite works.