You asked us, "What keeps satellites from falling out of the sky?"
Over the last half-century, more than 2,500 satellites have followed the first one into space. What keeps them all afloat is a delicate balance between a satellite's speed and the pull of gravity.
Satellites are basically continuously falling. Crazy, right?
But if they're moving at the right speed, they fall at the same rate that the curve of the Earth falls away from them. Which means instead of hurtling farther out into space or spiraling down to Earth, they hang out in orbit around the planet.
Adjustments are often needed to keep a satellite on the straight and narrow.
You see, Earth's gravity is stronger is some places than others. And satellites can get pulled around by the sun, the moon, even the planet Jupiter.
As if gravity weren't enough to deal with, satellites in low earth orbit -- like the Hubble Space Telescope - can also get pulled out of their orbit by drag from the atmosphere.
Not to mention the constant game of Frogger that satellites have to play to avoid space junk and other high flyers.