Echo
Echo either of two experimental communications satellites launched into orbit around Earth by the NASA during the 1960s. Consisting of aluminum-coated Mylar balloons that were inflated after launching, the Echo satellites were passive instruments—i.e., they simply reflected radio waves back to Earth rather than actively receiving, amplifying, and retransmitting them. The concept of using orbital satellites to relay communications predated space travel. With the launching of Sputnik 1, Earth's first artificial satellite, in 1957, interest quickly developed in orbiting communications satellites.
