A number of satellite system techniques have been suggested as candidates to provide ATC surveillance, communication, and/or navigation service over CONUS. All techniques perform postion determination by multilateration using a constellation of satellites. They can be categorized as follows: 1) Coordinated Aircraft-to-Satellite Techniques (CAST), 2) Random Access Aircraft-to-Satellite Techniques (RAST), and 3) Satellite-to-Aircraft Techniques (SAT). A technical assessment is made of the various techniques with no one particular technique emerging as superior; several feasible alternatives are identified. The assessment indicates that satellite bases techniques for CONUS ATC can be developed without relying on high risk technology. This volume deals with CAST, RAST and SAT are treated in companion volumes. A system employing CAST could operate by having each aircraft transmit only in response to interrogation from a satellite. The position of the aircraft is then obtained by multilateration using the arrival times of its response at coordinating the interrogations, mutual interference between different response can be avoided. The critical technical aspects of CAST are explored with special emphasis on signaling formats, avionics, the satellite antenna and susceptibility to jamming.