Project Echo was the first passive communications satellite experiment. Each of the two American spacecraft, launched in 1960 and 1964, were metalized balloon satellites acting as passive reflectors of microwave signals. Communication signals were transmitted from one location on Earth and bounced off the surface of the satellite to another Earth location.
Echo 1 sits fully inflated at a Navy hangar in Weeksville, North Carolina.
Echo 2
Holmdel Horn Antenna, constructed for Project Echo, and later used to discover the cosmic microwave background radiation.
T. Keith Glennan shows LBJ aluminized Mylar film used to make Echo I
A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a transponder; it creates a communication channel between a source transmitter and a receiver at different locations on Earth. Communications satellites are used for television, telephone, radio, internet, and military applications. Many communications satellites are in geostationary orbit 22,236 miles (35,785 km) above the equator, so that the satellite appears stationary at the same point in the sky; therefore the satellite dish antennas of ground stations can be aimed permanently at that spot and do not have to move to track the satellite. Others form satellite constellations in low Earth orbit, where antennas on the ground have to follow the position of the satellites and switch between satellites frequently.
Replica of an Iridium satellite
Replica of Sputnik 1
The Atlas-B with SCORE on the launch pad; the rocket (without booster engines) constituted the satellite.
An Iridium satellite