Satellite telemetry, tracking and command system including: • a plurality of ground stations, each of which is located at a respective position on earth's surface and is adapted to, when a satellite is in a respective visibility region of the ground station, receive downlink signals carrying telemetry data from said satellite and transmit thereto uplink signals carrying one or more commands; • on-board units, each of which is installed on board a respective satellite and is adapted to - receive GNSS signals from one or more global navigation satellite systems, - compute, on the basis of the received GNSS signals, positions and velocities of said respective satellite, - store coverage data indicative of the positions of the ground stations on earth's surface and of the visibility regions of said ground stations; and • a network control center, that is connected to the ground stations through one or more Internet Protocol networks and is adapted to - receive commands for satellites through the Internet Protocol network(s) from satellite operators that own/manage, each, one or more respective satellites, - provide, through the Internet Protocol network(s), the ground stations with the commands for the satellites, - receive, through the Internet Protocol network(s), from said ground stations, the telemetry data sent by the satellites, and - provide, through the Internet Protocol network(s), each satellite operator with the telemetry data sent by the respective satellite(s); characterized in that each on-board unit is further adapted to: • determine when said respective satellite is within the visibility region of one of the ground stations on the basis of the satellite's positions and velocities computed and of the stored coverage data; • when said respective satellite is within the visibility region of a ground station, transmit to said ground station the downlink signals and receive therefrom the uplink signals; and • carry out actions/operations corresponding to the commands received from the ground stations. • a plurality of ground stations, each of which is located at a respective position on earth's surface and is adapted to, when a satellite is in a respective visibility region of the ground station, receive downlink signals carrying telemetry data from said satellite and transmit thereto uplink signals carrying one or more commands; • on-board units, each of which is installed on board a respective satellite and is adapted to - receive GNSS signals from one or more global navigation satellite systems, - compute, on the basis of the received GNSS signals, positions and velocities of said respective satellite, - store coverage data indicative of the positions of the ground stations on earth's surface and of the visibility regions of said ground stations; and - receive GNSS signals from one or more global navigation satellite systems, - compute, on the basis of the received GNSS signals, positions and velocities of said respective satellite, - store coverage data indicative of the positions of the ground stations on earth's surface and of the visibility regions of said ground stations; and • a network control center, that is connected to the ground stations through one or more Internet Protocol networks and is adapted to - receive commands for satellites through the Internet Protocol network(s) from satellite operators that own/manage, each, one or more respective satellites, - provide, through the Internet Protocol network(s), the ground stations with the commands for the satellites, - receive, through the Internet Protocol network(s), from said ground stations, the telemetry data sent by the satellites, and - provide, through the Internet Protocol network(s), each satellite operator with the telemetry data sent by the respective satellite(s); - receive commands for satellites through the Internet Protocol network(s) from satellite operators that own/manage, each, one or more respective satellites, - provide, through the Internet Protocol network(s), the ground stations with the commands for the satellites, - receive, through the Internet Protocol network(s), from said ground stations, the telemetry data sent by the satellites, and - provide, through the Internet Protocol network(s), each satellite operator with the telemetry data sent by the respective satellite(s); • determine when said respective satellite is within the visibility region of one of the ground stations on the basis of the satellite's positions and velocities computed and of the stored coverage data; • when said respective satellite is within the visibility region of a ground station, transmit to said ground station the downlink signals and receive therefrom the uplink signals; and • carry out actions/operations corresponding to the commands received from the ground stations.