ECHO

either of two experimental communications satellites launched into orbit around the Earth by the National Aeronautics and Space Administration (NASA) during the 1960s. Consisting of aluminum-coated Mylar balloons that were inflated after launching, the Echo satellites were passive instrumentsi.e., they simply reflected radio waves back to Earth rather than actively receiving, amplifying, and retransmitting them. Nevertheless, by proving the concept of relaying radio signals through space, and by demonstrating the effectiveness of current satellite-tracking and other ground-station technologies, they stimulated a great deal of interest in the development of active satellite communication. Echo 1, launched on Aug. 12, 1960, inflated to a diameter of 100 feet (30 m). The satellite was placed in an almost circular orbit at an altitude of approximately 1,000 miles (1,600 km). At this height it circled the Earth every two hours. The first transmissions reflected off its surface were conducted between a terminal built by Bell Laboratories in Holmdel, N.J., and another terminal built by NASA's Jet Propulsion Laboratory in Goldstone, Calif. Echo 1 was used for experimental telephone, data, and facsimile transmissions. Signals were detected in Europe, although no messages were transmitted across the ocean. The satellite remained in orbit for almost eight years and was visible as a rapidly moving star in the evening skies. Echo 2, launched on Jan. 25, 1964, was 135 feet (about 40 m) in diameter. Its purpose largely was one of testing the dynamics of larger spacecraft, though it also was the focus of the first space venture involving cooperation between the U.S.S.R. and the United States. A radio signal transmitted from the Jodrell Bank Observatory, near Manchester, Eng., was reflected off Echo 2 and received at the Zimenki Observatory, near Gorky, Russia, U.S.S.R. (now Nizhny Novgorod, Russia). The satellite remained in orbit for five years. in Greek mythology, a mountain nymph, or oread. Ovid's Metamorphoses relates that Echo offended the goddess Hera by keeping her in conversation, thus preventing her from spying on one of Zeus' amours. To punish Echo, Hera deprived her of speech, except for the ability to repeat the last words of another. Echo's hopeless love for Narcissus, who fell in love with his own image, made her fade away until all that was left of her was her voice. According to the Greek writer Longus, Echo rejected the advances of the god Pan; he thereupon drove the shepherds mad, and they tore her to pieces. Gaea (Earth) buried her limbs but allowed her to retain the power of song.