This paper aims at presenting obtained results coming from an extensive simulations campaign of main Mobile Satellite Systems, MSS. This campaign was performed with the WORM (Write Once, Read Many) software simulation tool, developed by the authors, and exposed in previous conferences. The simulations deal with Non-GEO satellite constellations and provide performance evaluation for traffic loads generated simultaneously by fixed and mobiles user earth terminals. Some particular geographic distributions of generated traffic have been selected, in order to reflect a realistic traffic generation as anticipated for such satellite systems and services.