““The cheapest orbit available is LEO (Low Earth Orbit). People often think that "orbit" means there's no gravity. This is incorrect. In fact, the International Space Station (which is in LEO right now) is usually around 250 miles high and experiences about 90% of the gravity you experience on Earth. So why do the astronauts float around like there's no gravity? Although they are pulled toward the Earth all the time, they always "miss" it. Think of it like this: Imagine you fire a cannonball from the top of a tower. If you fire it softly, the ball will go a little ways then fall to the ground. If you fire it incredibly fast, it will just fly off into space. But between falling right down and going off into space, there are a lot of intermediate regimes. For a given height, there is some speed that is slow enough that it can't leave Earth, but fast enough that you'll never plop to the ground. If you were ridong that cannonball, you'd be falling, because gravity is tugging you down. At the same time, because you're going so fast, you'd be able to see Earth's curve. As you move from a point on the globe in a straight line, Earth curves down and away from you, increasing your distance from the surface. At this particular speed, you have two balanced effects: Gravity wants you down low, but your speed keeps you up high. So you just keep going around and around. You "orbit.””
