Link strategy for the mobile satellite system Iridium

This paper develops crosslink routing strategies for the mobile satellite system Iridium. Motorola´s Iridium satellite constellation, based on the orbit design of Adams and Rider [1987] is to provide a mobile satellite service for hand-held personal telephones. The Iridium system will have 66 satellites in 6 orbital planes at an altitude of h=780 km and a minimum elevation angle of θ=8.2 degrees for an optimal satellite distribution around the globe. It will be a system with direct connections between satellites (intersatellite links ISLs). These connections can be established with intra-orbit ISLs and with inter-orbit ISLs. The problem of routing messages through the satellite network is complicated by the time-varying satellite system geometry. The relative motion between the synchronized orbital planes is relatively small. However, orbital planes 1 and 6 are counterrotating and have large relative motion. Different inter-orbit ISL routing strategies are needed for these two cases. The time-varying behaviour of relative azimuth and elevation angles between satellites is analysed. Time-varying routing and antenna pointing angles are developed for both synchronized and counterrotating orbital places