Doppler Satellite Positioning, Telemetry and Data Systems

Before we consider the GPS system and its international equivalents, there are still two operating satellite systems that rely on the Doppler technique originally developed for Transit. These are very little known but provide important capabilities. These are the Argos environmental data system and the Cospas-Sarsat satellite search and rescue system. These systems, while not generally well known, provide excellent capabilities and operate in a spirit of international cooperation and collaboration for the benefit of all humankind. This chapter will present what these systems are, how they work, what they are used for, and the future directions for these.