Earth Observation Satellites 1957 to the Present
Earth observation satellites are used to map and monitor our planet’s resources and ever-changing chemical life cycles. They follow sun-synchronous, polar orbits. Under constant, consistent illumination from the sun, they take images in different colors of visible light and non-visible radiation. Computers on Earth combine and analyze the pictures. Scientists use Earth observing satellites to locate mineral deposits, to determine the location and size of freshwater supplies, to identify sources of pollution and study its effects, and to detect the spread of disease in crops and forests.
In 1955, the United States and the Soviet Union announced plans to launch artificial satellites. On October 4, 1957, the Soviet Union launched Sputnik 1, the first artificial satellite. It circled Earth once every 96 minutes and transmitted radio signals that could be received on Earth. On November 3, 1957, the Soviets launched a second satellite, Sputnik 2. It carried a dog named Laika, the first animal to soar in space. The United States launched its first satellite, Explorer 1, on January 31, 1958, and its second, Vanguard 1, on March 17, 1958.
In August 1960, the United States launched the first communications satellite, Echo I. This satellite reflected radio signals back to Earth. In April 1960, the first weather satellite, Tiros I, sent pictures of clouds to Earth. The U.S. Navy developed the first navigation satellites. The Transit 1B navigation satellite first orbited in April 1960. By 1965, more than 100 satellites were being placed in orbit each year.
Since the 1970’s, scientists have created new and more effective satellite instruments and have made use of computers and miniature electronic technology in satellite design and construction. In addition, more nations and private businesses have begun to purchase and operate satellites. By the early 2000’s, more than 40 countries owned satellites, and nearly 3,000 satellites were operating in orbit.