The Global Communication Network (GCN) is a new concept that uses polar-orbiting satellites to provide communications services that are unavailable otherwise from existing satellite systems. These services are becoming essential to perform the kind of global science that has been proposed for the 1990s and beyond by the ocean, atmosphere, and earth processes science communities. Existing communications services over the oceans and particularly over the polar regions are severely constrained. Service Argos provides worldwide data collection capability at low rates and for limited quantities of data, but it makes no provisions for interrogation or for wide band, high-volume data [see In Situ Ocean Science Working Group, 1985]. Other geostationary satellite systems, such as the Geostationary Operational Environment Satellite (GOES), require an amount of transmission power that is prohibitive for most mobile, floating, or airborne users [see Hughes Aerospace Corporation, 1980].