Ercetin, OzgurBall, Michael O.Tassiulas, LeandrosThe US airspace is reaching its capacity with the current Air Traffic Control system and a number of flights that is constantly rising, and estimated to be over 54 million per year by 2002. The FAA has undertaken several projects to modernize the National Airspace System (NAS) to ensure the safety of the increasing number of flights. Of special importance is the modernization of the Air-Ground (A/G) Communications infrastructure, which is the heart of the air traffic control (ATC). <p>The current plan in the modernization of the A/G communications is to migrate from analog voice only system to integrated digital voice and data system. The next generation satellite systems can be an alternative to the terrestrial A/G systems by their low propagation and transmission delays, global coverage, high capacity, and free flight suitable characteristics. In this paper, we give an overview of the current and the future ATC architectures, describe the systems and the communications issues in these systems, and develop a framework in which LEO/MEO next generation satellite systems can be integrated to the future ATC systems.en-USdigital communicationsmulti-user systemsnetwork managementLow Earth Orbit satellitesLEOGEOMEOair traffic controlaeronautical communicationsSystems Integration MethodologyTechnical Report