November 24, 2012 12:58 am

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How does a television signal get to the other side of the world in seconds? What tells ships exactly where they are in the middle of the ocean? How do we get warning that storms are coming? Satellites do all these things and more.
Satellites are objects in outer that fly around planets in circular paths called orbits. Artificial satellites are made by people. Thousands of satellites are zooming around our planet right now.
The Soviet Union launched the first artificial satellite, Sputnik 1, in 1957. Sputnik 1 broadcasted a steady signal of beeps. It circled Earth for three months and then fell back into the atmosphere and burned up. The atmosphere is the air that surrounds Earth.
Satellites need to reach a height of at least 120 miles (200 kilometers) to orbit. They also need to travel faster than 18,000 miles per hour (29,000 kilometers per hour). A satellite any lower or slower would soon fall back down to Earth. It takes a rocket to bring satellites up to that height and speed.
Most satellites are launched from the ground. Some small satellites can be launched from high-flying planes. This uses less fuel.
Other satellites are launched using a space shuttle or other piloted rocket. This way, astronauts on the space shuttle can make sure the satellite is working and gets into the right orbit.
Satellites are used for a great many things. Communications satellites beam TV, radio, and telephone signals all around the world. Navigational satellites help people know where they are and get where they are going. Weather satellites take pictures of clouds and storms from above to help make weather forecasts. Spy satellites look down and snoop on other countries. Other satellites help scientists to study Earth and other planets.
Space is a difficult place to be. You can’t plug in a cord in outer space, so satellites need to take a power source with them. It’s hard to get satellites pointed in the right direction because there’s nothing to turn them with. Satellites need to work in the freezing cold of Earth’s shadow as well as in the blazing heat of the Sun’s rays. They also need to be tough enough to survive collisions with tiny asteroids (space rocks)!
Most satellites use both power from the Sun and batteries to work. They catch the Sun’s energy using large flat solar panels. Satellites keep these panels pointed at the Sun. They use batteries when the Sun doesn’t shine on them.
Satellites can stay pointed in the right direction using small rockets called attitude thrusters. They can also use instruments called gyroscopes. Sometimes magnets on board the satellite can push against the magnetic field of Earth to aim the satellite correctly.
No air flows past satellites to cool them. To keep from getting too hot in the Sun, satellites have panels that open and close. This lets heat escape. Satellites often spin so the Sun doesn’t make one side so hot that it melts.
Satellites also need to be made from strong materials in case tiny asteroids hit them. They need materials that don’t become brittle in the cold and the harsh radiation of space.
When satellites stop working they are often left in orbit as so much space junk. Others drift too low to keep orbiting and burn up as they fall. Still others are brought back to Earth for repairs.
Nonworking satellites are sometimes sent down from orbit into the atmosphere to burn up on purpose. Space is very large, but still scientists need to be careful that satellites don’t crash into each other. They try to get rid of the broken ones.
Since Sputnik 1, more than 5,000 satellites from many countries have been launched. Artificial satellites now orbit the Sun, Mars, Venus, and other planets and their moons. Most satellites, however, orbit Earth. High above your head thousands of satellites circle the planet every day.
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