Montreal Space Symposium

Today, the Global Positioning System (GPS) developed by the U.S. Department of Defense is essential for countless applications. Of course, it provides good positioning (~m) for vehicles or pedestrians, but it can also provide very precise positioning (~dm or cm) for surveying or agriculture. Not forgetting the transmission of a very accurate time (~ns) for communication systems or financial networks.
Also, from almost the beginning of the GPS, the question of its use in space was studied, but it took some time and experience before its actual use. Today, it is common to find GPS receivers on board low Earth orbit (LEO) satellites, and a lot of research and development is going on regarding its use in higher orbits, even above the GNSS constellations. To date, the farthest position obtained thanks to GPS was at an altitude around 150 000 km.
Now, with the availability of three other global navigation satellite systems (GNSS), namely GLONASS (Russia), Galileo (Europe) and BeiDou (China), and the availability of civilian signals on several frequencies, the use of navigation satellite systems will continue growing, offering better performance and better security.
In this talk, we will first present the GNSS, with a brief history, the current status of the different systems, a summary of their applications, a description of the space segment, and an introduction to the GNSS signals and the basic operation of a GNSS receiver.
In a second part, we will focus on the use of GNSS in space, describing the different challenges, namely the very weak signals, the unfavorable geometry and the high dynamics.