The orbit of a Global Positioning System (GPS) satellite is disturbed by solar radiation pressure (SRP) inside sun lights. When the satellite passes the shadow of Earth or Moon, the SRP does not affect the satellite due to sun lights’ absence. To determine the precise GPS orbits, the shadow of Earth and Moon should be considered. Therefore, we studied the Earth and Moon shadow phenomenon on the GPS satellites. Using the conical shadow model, we have analyzed how much time entire satellites experience the shadow. Furthermore, we studied the effect Moon shadow with the accuracy on the precise GPS orbits. For this analysis, Seoul national university orbit determination tool (SNUOD) tool was used as the orbit filter. It utilizes extended Kalman filter to estimate precise GPS orbits using double-differenced carrier phase observations of international global navigation satellite system service (IGS) network. The filter was verified with the IGS final orbits.

Keywords: shadow of Earth, shadow of Moon, GPS orbits