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3.3 Scientific research satellites (commercial and noncommercial)ġU CubeSat ESTCube-1, developed mainly by the students from the University of Tartu, carries out a tether deployment experiment in low Earth orbit.Satellite subsystems attend many tasks, such as power generation, thermal control, telemetry, attitude control, scientific instrumentation, communication, etc. Satellites are usually semi-independent computer-controlled systems. Some are launched at sea from a submarine or a mobile maritime platform, or aboard a plane (see air launch to orbit). Usually, it lifts off from a launch pad on land. Well-known (overlapping) classes include low Earth orbit, polar orbit, and geostationary orbit.Ī launch vehicle is a rocket that places a satellite into orbit. Satellite orbits have a large range depending on the purpose of the satellite, and are classified in a number of ways. Satellites can operate by themselves or as part of a larger system, a satellite formation or satellite constellation. Space stations and human spacecraft in orbit are also satellites. Common types include military and civilian Earth observation satellites, communications satellites, navigation satellites, weather satellites, and space telescopes. Among several other applications, they can be used to make star maps and maps of planetary surfaces, and also take pictures of planets they are launched into. Over a dozen space probes have been placed into orbit around other bodies and become artificial satellites of the Moon, Mercury, Venus, Mars, Jupiter, Saturn, a few asteroids, a comet and the Sun. Ī few large space stations, including the International Space Station, have been launched in parts and assembled in orbit. In terms of countries with the most satellites, the United States has the most with 2,944 satellites, China is second with 499, and Russia third with 169. Approximately 63% of operational satellites are in low Earth orbit, 6% are in medium-Earth orbit (at 20,000 km), 29% are in geostationary orbit (at 36,000 km) and the remaining 2% are in various elliptical orbits. Of those, about 1,900 were operational, while the rest had exceeded their useful lives and become space debris. According to a 2018 estimate, about 5,000 remained in orbit. Since then, about 8,900 satellites from more than 40 countries have been launched. On 4 October 1957, the Soviet Union launched the world's first artificial satellite, Sputnik 1. These objects are called artificial satellites to distinguish them from natural satellites such as Earth's Moon. In the context of spaceflight, a satellite is an object that has been intentionally placed into orbit.
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A full-size model of the Earth observation satellite ERS 2