The most common use for satellites in this region is for navigation, communication, and geodetic/space environment science. The most common altitude is approximately kilometre (mi)), which yields an orbital period of 12 hours, as used, for example, by the Global Positioning System (GPS). Other satellites in medium Earth orbit include Glonass (with an altitude of kilometre (mi)) and Galileo (with an altitude of kilometre (mi)) constellations.}}[citation needed] Communications satellites that cover the North and South Pole are also put in MEO.