该卫星系统由轨道上的四颗卫星组成,其中两颗服现役;第三颗为西联星,提供商业通信业务;第四颗为备用星。该系统将于1980年正式投入使用。由于此系统轨道较高,所以它对低高度和中高度的卫星覆盖极好。一旦投入使用后,航宇局将关闭除跟踪高轨道卫星和深空飞行外,所不需要的地面站,这样能节省很多的资金。 The satellite system consists of four satellites in orbit, of which two are active; the third is Western Union, providing commercial communications services; the fourth is a spare star. The system will be officially put into use in 1980. Because of its high orbit, it has excellent coverage of low and medium altitude satellites. Once put into service, the NASA will close down unwanted ground stations other than tracking high orbiting satellites and deep space flights, thus saving a lot of money.