Medium earth orbit (MEO) satellites orbit the earth between low earth orbit (LEO) and geostationary orbit, providing better coverage for wireless communications. They orbit between 1000-22,000 miles above the earth and typically have elliptical orbits. MEO satellites are used in navigation systems such as GPS and Glonass, and a proposed MEO navigation system for the European Union called Galileo is expected to go online in 2013.
A medium earth orbit (MEO) satellite is a satellite that orbits the earth among the low earth orbit (LEO) satellites, which orbit the earth at a distance from earth of about 200-930 miles (321.87-1496.69 km) and those satellites that orbit the earth in a geostationary orbit, approximately 22,300 miles (35,888.71 km) above the earth. Each type of satellite can provide a different type of coverage for wireless communications and devices. Like LEOs, these satellites do not maintain a stationary distance from the earth. This is in contrast to geostationary orbit, where satellites are always approximately 22,300 miles from the earth.
Any satellite that orbits the earth between about 1000-22,000 miles (1609.34-35,405.57 km) above the earth is a MEO. Typically the orbit of a satellite in medium Earth orbit is about 10,000 miles (16,093.44 km) above the earth. In various designs, these satellites make the trip around the earth in between 2 and 12 hours, which provides better coverage for larger areas than that provided by LEOs.
In 1962, the first communications satellite, Telstar, was launched. It was a medium-Earth orbit satellite designed to help facilitate high-speed telephone signals, but scientists soon learned what some of the problematic aspects of a single MEO in space were. It only provided transatlantic telephone signals for 20 minutes of each approximately 2.5-hour orbit. It was apparent that multiple MEOs needed to be used to provide continuous coverage.
Since then numerous companies have launched both LEO and MEO. You need about two dozen LEOs to provide continuous coverage and fewer MEOs. However, LEOs typically orbit in a circular pattern around the equator. A satellite in medium Earth orbit can have a variety of different orbits, including elliptical ones, and can provide better overall satellite communications coverage if there are enough of them and the orbit is rapid. The earth’s cover is called a footprint and MEOs are typically able to create a larger footprint due to their different orbital patterns and because they are taller than LEOs.
Today the medium earth orbit satellite is most commonly used in navigation systems around the world. These include the Global Positioning System (GPS) and Russian Glonass. A proposed MEO navigation system for the European Union called Galileo is expected to go online in 2013.
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