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A satellite is any object that goes around and around a larger object in space. Some satellites are natural. For example, the Moon is a satellite because it goes around and around the Earth. Other satellites, such as the International Space Station, are made by humans. Such human-made objects are referred to as "artificial satellites."

Generally, when people talk about satellites, they have in mind a human-made machine that is launched into space in order to perform one or more specific tasks, such as to relay communications, take pictures, or monitor the Earth's environment.

No one knows who first had the idea of satellites, but the first human-made object put into space was called "Sputnik," which was launched by the Soviet Union on October 4, 1957 . "Sputnik" means "companion" or "fellow traveler" in Russian. It was launched into a low-Earth orbit barely above the Earth's atmosphere. It was not used for two-way communications since it could only transmit a signal to Earth.

Many satellites followed Sputnik into low-Earth orbit. The first satellite dedicated to communications was called ECHO and was launched by the United States in 1960. It was a "passive" satellite that connected users by bouncing radio signals off of its surface. It did not transmit radio signals itself.

The first "active" communication satellites were the TELSTAR and RELAY satellites, which were launch by the United States in 1962. These satellites received radio signals from Earth and amplified the signals (that is, made them stronger) before re-transmitting them back to Earth. The amplification of the radio signal made these communications more reliable and robust than communications by passive satellites.

The first satellite to use geostationary orbit for communications was called "Syncom" and was launched by the United States in 1963. Syncom weighed 78 pounds and was 28 inches in diameter. A geostationary satellite orbits the Earth at a much higher altitude than low-Earth orbit satellites. The concept of geostationary satellites used for communications is credited to an article written in 1945 by Arthur C. Clarke in the British radio magazine Wireless World . In the article, Clarke suggested that a satellite in geostationary orbit would appear fixed in the sky with respect to a certain point on the Earth's surface, and that a network of three satellites in such an orbit could enable communications to practically any point in the world, except the polar regions. For this reason, Arthur C. Clarke is often credited as the inventor of satellite communications.

Satellites come in all sizes. Some satellites are built by amateur operators and can be very small, less than one cubic foot! Other satellites are much larger. Modern communications satellites can weigh up to six tons and be the size of a small school bus. In order to give some idea of the size of modern communications satellites, here are some pictures of communications satellites as they are being built. Looking at the people in the pictures can give you an idea of the size of the satellites!

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Question 1
Why is the Moon a satellite?
A. because it has less surface gravity than that of the EarthB. because it is close to the Earth
C. because it goes around and around the EarthD. because the Earth goes around and around the Moon
Question 2
What was the first human-made object put into space called?
A. ColumbusB. Sputnik
C. CassiniD. Hubble
Question 3
When was the first artificial satellite launched into space?
A. 1950B. 1977
C. 1957D. 1937
Question 4
Which fact about Sputnik is NOT correct?
A. It was the first human-made object put into space.B. It was launched by the Soviet Union.
C. It was launched into a low-Earth orbitD. It was used for two-way communications.
Question 5
What was the first satellite dedicated to communications?
Question 6
Which of these was a "passive" sattellite?
C. RELAYD. All of the above
Question 7
What made the TELSTAR and RELAY satellites more reliable and robust?
A. Modulation of the radio signalB. Geostationary orbit for communications
C. The amplification of the optical signalD. The amplification of the radio signal
Question 8
Which of the following was the first satellite to use geostationary orbit for communications?
A. SytcomB. Syncom
C. RelayD. Orsted
Question 9
What is Wireless World?
A. an active satelliteB. British radio station
C. British radio magazineD. U.S radio magazine
Question 10
How much do modern communications satellites weigh?
A. up to six poundsB. up to sixteen tons
C. up to 6000 poundsD. up to six tons
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