inks (ISL) is to provide true global coverage in which a satellite can provide service without need for simultaneous contact with a gateway, such as over the oceans, and to reduce the total number of gateways necessary to support the network. The redundancy available through diversity of communications channels in the space network enables continued utilization of the system in case of gateway outage. These benefits indicate the advantages from a logical networking perspective. Figures 2-3 and 2-4 depict an intersatellite linked constellation. Orbit, Fixed Mobile network network Figure 2-3. Intersatellite Link (ISL) System [Richharia95] Intersatellite Links Public Telephone Gateways Mobile Control Facilities Users Telephones Stations Figure 2-4. Personal / Mobile Intersatellite Linked System [Jamalipour98] The disadvantages of intersatellite links arise mostly from consideration of the physical satellite engineering perspective, resulting in increased complexity of the satellite payload. Implementation of intersatellite communications links requires space vehicle attitude stability and antenna tracking and pointing control to establish RF links and to compensate for large Doppler shifts at high latitudes. Large on-board processing loads result from management and switch routing of traffic within the payload. The Iridium mobile telephony constellation has deployed an intersatellite networked constellation and ISL implementations are planned for LEO broadband satellite constellations. Orbit Architecture of Telecommunications Constellations [Gordon 93] Low-earth orbit satellites typically refer to orbit altitudes between 500 km and 2000 km, and inclination angles between 30° and 90°. LEO satellites are normally launched into their operational plane at a parking altitude of 300 km to 400 km and elevated to mission altitude using spacecraft propulsion. Initial active communications satellites launched in 1962, Telstar and Relay, were placed into LEO orbits due to constraints on launch vehicle performance. Although man