在卫星的各种实际应用中,包括通信、导航、预警、测地、侦察和气象等,都希望在轨道上同时有几颗卫星,组成卫星群或称卫星星座。通常主张用三颗静止轨道卫星组成星座来覆盖地面,但是实际上这种星座只能覆盖低纬度和中纬度区域,不能覆盖高纬度地区,特别是地球两极区域。 In various practical applications of satellites, including communications, navigation, early warning, geodesy, reconnaissance and meteorology, it is hoped that there will be several satellites in orbit at the same time to form satellite constellations or satellite constellations. It is usually advocated that three constellations of orbit satellites form a constellation to cover the ground, but in fact this constellation covers only the low-latitude and mid-latitude regions and can not cover high latitudes, especially the polar regions of the Earth.