Agena launch vehicle. In addition to passive communications experiments, it was used to investigate the dynamics of large spacecraft and for global geometric geodesy. Since it was larger than Echo 1A and orbiting in a near-polar orbit, Echo 2 was conspicuously visible to the unaided eye over all of the Earth. It reentered Earth's atmosphere and burned up on 7 June 1969. Both Echo 1A and Echo 2 experienced a solar sail effect due to their large size and low mass. Later passive communications satellites, such as OV1-08 PasComSat, solved the problems associated with this by using a grid-sphere design instead of a covered surface. Later yet, NASA abandoned passive communications systems altogether, in favor of active satellites. Legacy Project Echo facilitated the first successful satellite transmission and first two way communications between the JPL Goldstone facility and Bell Telephone Laboratories facility in Holmdel, New Jersey. Other groups participated in experiments including the Collins Radio Company and the Naval Research laboratory. Because Echo was only a passive system, it was primarily useful in demonstrating the future potential of satellite communications and became obsolete before it deorbited in 1968. Echo was most known to the general public for its visibility as it could be seen at night with the naked eye. The Echo satellite program also provided the astronomical reference points required to accurately locate Moscow. This improved accuracy was sought by the U.S. military for the purpose of targeting intercontinental ballistic missiles. The large horn antenna at Holmdel constructed by Bell Labs for the Echo project was later used by Arno Penzias and Robert Woodrow Wilson for their Nobel Prize-winning discovery of the cosmic microwave background radiation. On 15 December 1960, the U.S. Post Office issued a postage stamp depicting Echo 1. Gallery See also AO-51, AMSAT-OSCAR 51 (also known as Phase 2E, or ECHO) – an amateur radio communications satellite launched in 2004 Courier 1B – world's first active repeater satellite, launched in 1960 List of communications satellite firsts PAGEOS – a similar balloon satellite project Project SCORE – world's first communications satellite, launched in 1958 Telstar – first active, direct relay communications satellite, launched in 1962 TransHab, a subsequent expandable spacecraft technology project pursued by NASA U.S. space exploration history on U.S. stamps Norman L. Crabill References Further reading Nick D'Alto "The Inflatable Satellite", Invention and Technology Summer 2007, Volume 23, Number 1, pp. 38–43 External links 1960