What is Satellites

This chapter focuses on satellite mega-constellations, as mega-constellations raise several technical issues from telecommunication to launching these huge sets of satellites. Through an overview of basic signal science (periodic waves, types of modulation) and a discussion about telecommunication systems, actual 4G and future 5G networks, the chapter aims at giving without prior scientific background, sufficient material to better understand mega-constellation from its basic functioning to sophisticated satellites systems on orbit providing wide communication services all around the Earth. Major topics are evoked about such constellations be it on launching, space debris, challenges, and technologies used from a technical point of view.