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Why don’t satellites fall out of the sky?
A satellite is a type of machine that orbits Earth, taking pictures and collecting information. There are thousands of satellites orbiting Earth right now.
How do they all stay up there—and why don’t they just fall out of the sky?
If you throw a ball into the air, the ball comes right back down. That’s because of gravity—the same force that holds us on Earth and keeps us all from floating away.
To get into orbit, satellites first have to launch on a rocket. A rocket can go 25,000 miles per hour! That’s fast enough to overcome the strong pull of gravity and leave Earth’s atmosphere. Once the rocket reaches the right location above Earth, it lets go of the satellite.
The satellite uses the energy it picked up from the rocket to stay in motion. That motion is called momentum.
But how does the satellite stay in orbit? Wouldn’t it just fly off in a straight line out into space?
Not quite. You see, even when a satellite is thousands of miles away, Earth’s gravity is still tugging on it. That tug toward Earth--combined with the momentum from the rocket causes the satellite to follow a circular path around Earth: an orbit.
When a satellite is in orbit, it has a perfect balance between its momentum and Earth’s gravity. But finding this balance is sort of tricky.
Gravity is stronger the closer you are to Earth. And satellites that orbit close to Earth must travel at very high speeds to stay in orbit.
For example, the satellite NOAA-20 orbits just a few hundred miles above Earth. It has to travel at 17,000 miles per hour to stay in orbit.
On the other hand, NOAA’s GOES-East satellite orbits 22,000 miles above Earth. It only has to travel about 6,700 miles per hour to overcome gravity and stay in orbit.
Satellites can stay in an orbit for hundreds of years like this, so we don’t have to worry about them falling down to Earth.
Find out more about our home planet at NOAA SciJinks.