Meridian navigation satellite is a series of American low-orbit navigation satellites, also known as naval navigation satellite system. Its main function is to provide high-precision intermittent two-dimensional positioning for nuclear submarines and various surface ships for offshore oil exploration, marine survey and positioning, land user positioning and geodesy (determination of pole shift, earth shape and gravity field). The satellite meridian adopts a nearly circular polar orbit with an altitude of about 1000 km, and adopts a dual-frequency Doppler velocimetry navigation system. This low orbit is used to avoid the attenuation of Doppler effect. A space navigation network (navigation constellation) around the earth is composed of 4-5 satellites with evenly separated orbital planes, so that navigation users anywhere in the world use satellite positioning 1.5 hours on average. The practical meridian satellite adopts gravity gradient stabilization to make the antenna face the ground. The satellite is equipped with a magnetic attitude control system, which enables the satellite gravity rod to capture the local gravity vertical line, and the damping ball at the rod end is used to damp the libration, and the orientation accuracy can reach 3 ~ 5. The improved satellites such as Nova are also equipped with offset momentum wheels for yaw control in the pitch direction, and the gravity rod is changed into scissors structure, so the accuracy of three-axis attitude control is better than 3.
The special equipment of meridian navigation satellite includes: crystal oscillator, navigation message memory and remote control receiver. The relative accuracy of meridian navigation satellite orbit parameter prediction is better than 5 meters, the absolute accuracy is better than 10 meters, and the navigation and positioning accuracy is generally 20 ~ 50 meters.