Satellite
NASA ‘s Earth-observing fleet as of June 2012. A full-size model of the Earth observation satellite ERS 2 In context of spaceflight , a satellite is an artificial object which has been intentionally placed into orbit . Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as Earth’s Moon . In 1957 the Soviet Union launched the world’s first artificial satellite, Sputnik 1 . Since then, about 6,600 satellites from more than 40 countries have been launched. According to a 2013 estimate, 3,600 remained in orbit. [1] Of those, about 1,000 were operational; [2] while the rest have lived out their useful lives and became space debris . Approximately 500 operational satellites are in low-Earth orbit , 50 are in medium-Earth orbit (at 20,000 km), and the rest are in geostationary orbit (at 36,000 km). [3] ...