History and general principles of GNSS

The space age began in 1957, with the launch of the first Sputnik satellite (USSR). The satellite emits a simple radio signal for several weeks. This signal, detectable by all, was observed by American military forces. Measuring the Doppler effect on this signal, the American army quickly imagined and developed a global positioning system for its navy and missile guidance: the Transit system was operational by the mid-1960s, with an accuracy of several hectometers and a response time of several hours. The next stage, still military, saw the parallel development in the USA and USSR of real-time metric precision systems, known as GPS (Global Positioning System, USA) and Glonass (Global Navigation Satellite System, USSR). The first satellites were launched at the end of the...