Long term evolution of the eccentricity in the MEO region: Semi-analytical and analytical approach

We study the long term evolution of the mean eccentricity of trajectories within the MEO region, and in particular at altitudes corresponding to Galileo nominal or disposal cases, following a semi-analytical and an analytical approach. The model accounts for all the significant perturbations acting on the trajectories: zonal and tesseral parameters of the Earth's gravity field, luni-solar attraction, atmospheric drag when relevant; we study the time evolution of the two components of the eccentricity vector, depending on the choice of the initial conditions: long period variations, that could even been seen as secular effects over some periods, are interpreted in terms of the influence of the luni-solar attraction. Maps of maximal eccentricity reached over less than 2 centuries are performed with the STELA s/w, and the role played by the ? + 2? resonance is underlined.