Comparison of the probability of visibility of the most important currently projected mobile satellite systems

During the next years a number of mobile satellite systems (MSS) for low Earth orbits (LEO) and for medium Earth orbits (MEO) will be available for global personal communications. The most important currently projected systems are Iridium, Globalstar, Odyssey, ICO (formerly Inmarsat-P), and Teledesic. These systems will provide mobile communication from any place on the Earth to any person at another place on the Earth. A main performance parameter of these systems is the visibility of satellites. Additionally for MSS without intersatellite links (ISLs) it is necessary, that a satellite always has one earth station in view. In this paper the probability of visibility for different elevation angles will be presented for the named systems. The connection between the probability of visibility, the elevation constraint and the service radius is shown for the named systems without ISLs (Globalstar, Odyssey, ICO).