English Essay on “Artificial Satellites
The first artificial satellite was launched on October, 4, 1957. Since that time, hundreds of other satellites have been launched, carrying all types of scientific and military equipment You need a powerful rocket to launch a satellite.
First the rocket must raise the satellite at least 100 miles above the earth's surface to avoid air resistance. Then it has to point the satellite horizontally and give it a speed of at least 5 miles per second. At that speed the satellite will keep revolving round the earth without need for further attention.
Because of the speed of the satellite, there is no danger of is falling down on the earth's surface and the earth's gravitational force is enough to keep the satellite from flying off into space.
A satellite orbit goes completely around the earth in the shape of an ellipse, which looks like a circle stretched at one side. The length of time a satellite takes to go around the earth depends on the size of its orbit. Satellites could stay in the air for hundreds of miles if it were not for air drag which brings it down gradually.
Since the lower layers of the atmosphere are denser, the life-time of a satellite depends mainly on its height. Satellites can be detected by visible light or by radio signals. To see a satellite, we must be in darkness while the satellite is in sunlight, so that the satellite is bright against a dark sky.
Most satellites carry radio transmitters so that their positions can be determined by marking the direction of the radio signals. Satellites are used for many different scientific purposes. Firstly, valuable information comes from just observing the satellite's motion.
The exact shape of the earth can be determined, because the satellite turns slowly because the attraction of the bulge around the earth's equator makes the orbit of a satellite turn. Also, they can carry measuring instruments, by which information can be obtained.
Astronomers hope that one day satellites will carry telescopes to observe the stars from outside the earth's atmosphere.
QUESTION
1. How are satellites useful?
2. How is a satellite launched?
3. What keeps the satellites from falling down on the earth's surface?
What brings down a satellite gradually? 5. What does the life time of a satellite depend on?