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The trajectory of GNSS satellites, and the visibilty conditions from the ground, can be carried out from precise GNSS measurements, or from the well-known Two-Line Elements (TLE) provided by NORAD. Depending upon the purpose, the latency of the tracking data, the time available to derive the results, precise orbits (at the level of one centimeter accuracy) or rough orbits can be propagated and delivered to the users, through a large set of various tools, some of them being publickly available. We propose in this paper to analyse the compatibility of different approches and different initial conditiond, propagated over very short ( a couple of days) and very long (two centirues) time scales, applied to some satellites in the various GNNS constellations (GPS, Galileo, GLONASS, BeiDou).
GRGS (Groupe de Recherche de Géodésie Spatiale) is a french research group gathering up french scientifists within different insitutions focusing their activitties to space data analysis, and in particular related to space geodesy and precise orbitography. Hence, GRGS is in charge of the french analysis center of GNSS data providing precise orbits of the GNSS satellites IGS, the International GNSS Service, as a component of the International Association of Geodesy. Using the time series of orbtal elements built by GRGS is is way to take benefit of the best possible accuracy to the tracking data.
As a first part of this presentation, we analyse over a couple of days the visibility conditions as scheduled from precise orbits and from TLE time series, that have the state of "mean elements », with an accuracy which is quantified though through formulas deriving osculating elements from mean elements and conversely. As a second part of this presentation, the stability of GNSS orbits is analyzed over two centuries, to investigate from the TLE times series whether the future storage orbits are likely to be sensitive, or not, to deep resonance effects, by using the french STELA s/w designed in the framework of the french space operation act.
