The television we watch at home, the weather updates we receive, the knowledge we acquire of other planets in the universe, are all possible due to satellites. Artificial satellites are man-made objects that orbit the Earth. These satellites are launched for specific purposes. A satellite is lifted from the earth's surface by a rocket and, once placed in orbit, maintains its motion without further rocket propulsion. The first artificial satellite, Sputnik I, was launched on Oct. 4, 1957, by the USSR, which triggered the space race between the Soviet Union and the U.S. The first U.S. satellite, Explorer I, was launched on Jan. 31, 1958. During the first decade of space exploration, satellites were launched from either the United States or USSR. Today, there are more than three dozen launch sites in use or under construction in more than a dozen countries.

Communications satellites are stationed in space to provide a worldwide linkup of radio, telephone and television. Echo 1 was the first communications satellite to be launched in 1960. It was a large metal balloon that reflected radio signals striking it. The first commercial geosynchronous satellite, Intelsat 1 was launched in 1965.

There are very many different types of satellites and each one serves a different purpose. Earth observation satellites are specifically designed to observe the Earth. They are used for environmental monitoring, meteorology and map making. Astronomical satellites are used for observing distant planets, galaxies and other space objects. Navigation satellites were developed primarily to satisfy the need for a navigation system for nuclear submarines. Today they use radio time signals transmitted to enable mobile receivers on the ground to determine their exact location. Reconnaissance satellites are either observation or communication satellites deployed for military intelligence applications.

Weather satellites are used to monitor the weather and climate of the Earth.. They provide continuous, up-to-date information about large-scale atmospheric conditions such as cloud cover and temperature profiles. Tiros 1, was the first weather satellite that was launched in 1960.

Not so long ago, satellites were exclusive, top-secret devices. Today, they are an essential part of our daily lives.