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Space Sciences: Satellites - Lift Off!

Even if you jump as high as you possibly can, you know you're still going to fall back down to the ground. Gravity is the force that pulls all objects closer together, and it is always pulling you toward the center of the Earth (luckily the ground is nice and solid!). The more massive an object, the stronger its gravitational pull. The Earth's gravity is so strong it not only holds onto people, dirt, and satellites, but even things as light as our atmosphere.

If you want to get away from the Earth's gravity, you need to move really, really fast. To le ave the Earth and head off into space, maybe to visit the Moon or Jupiter, you need to exceed the Earth's escape velocity.

The escape velocity for the Earth is about 7 miles (11.2 km) per second that's 25,000 miles per hour! Escape velocity is different for each planet or moon because it depends on the mass and radius of each one. A basic physics equation can be used to calculate the escape velocity of any particular object in space.

Image of rocket launching
Courtesy of NASA

NASA astronauts in space shuttle
Courtesy of NASA

When we launch a satellite, we don't want it to go far from earth. Satellites must therefore reach a certain orbital velocity to balance between the forward speed that would send them off into space and the gravity that would pull them crashing to the ground. Satellites and the space shuttle are actually always falling toward the Earth, but their forward motion is fast enough that they are instead pulled into a nearly circular orbit around the planet. This is exactly how the Moon stays in orbit around the Earth, and the planets in orbit around the Sun. Astronauts in space are not really "weightless" although they feel light as air, they are really falling but constantly missing the Earth!
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