GPS主系统是居心叵测的老美发射运行的卫星系统，包含了27颗能持续发送地理位置海拔高度的卫星，24个正常使用，3个备用，这些卫星平均分布运行在六个轨道上。一般来说，在地面-GPS is the main system is very much ill-old US-run satellite launch system, contains 27 to continue to send location altitude satellites, 24 of normal use, three back-up, the average distribution of these satellites orbit in six runs. Generally speaking, on the ground