The computation of a navigation satellite position and clock is a general task in global positioning system (GPS)
positioning that is necessary to compute a user position. The data needed for this task can be obtained from a
broadcasted navigation message. A satellite orbit can be computed by using satellite orbital elements and
perturbations Users should use a precise ephemeris provided by the International GNSS Service (IGS) or National GeospatialIntelligence Agency (NGA). IGS is a voluntary federation of about 400 stations that provides GPS and GLONASS
precise ephemerides [1]. IGS orbit accuracy is believed to be less than 0.05m. The IGS precise ephemeris is
available in 15 minute intervals.