The BD 1 (Beidou 1) satellites were the 1st phase of the chinese Beidou (Compass) satellite navigation system. The first phase uses only geostationary satellites, in contrast to GPS and GLONASS. This reduces the number of satellites, but limits the coverage to a less than hemispherical area. The basic constellation requires 3 satellites. The satellites are based on the DFH-3 Bus.