Echo satellite

The Echo satellites were NASA's first passive communications satellite experiment. Each spacecraft was designed as a metallized balloon satellite acting as a passive reflector of microwave signals. Communication signals were bounced off of it from one point on Earth to another. [ [http://samadhi.jpl.nasa.gov/msl/QuickLooks/echoQL.html JPL The Mission and Spacecraft Library] ]

Echo 1

Following the failure of the Delta rocket carrying Echo 1 on May 13, 1960, Echo 1A (commonly referred to as just "Echo 1") was successfully put in a 1519 x 1687 km orbit on August 12, 1960. The 30.5 meter (100 foot) diameter balloon was made of 0.127 mm (0.005 inch) thick metallized Mylar polyester film and was successfully used to redirect transcontinental and intercontinental telephone, radio, and television signals. The satellite also aided the calculation of atmospheric density and solar pressure due to its large area-to-mass ratio. As its shiny surface was also reflective in the range of visible light, Echo 1A was visible to the unaided eye over most of the Earth. Brighter than most stars, it was probably seen by more people than any other man-made object in space. Echo 1A reentered Earth's atmosphere and burned up on May 24, 1968.

Echo 1 was a passive communications satellite: it functioned as a reflector, not a transmitter. After it was placed in a low orbit of the Earth, a signal would be relayed to Echo, reflected or bounced off its surface, then returned to Earth. Echo 1 was visible to the eye because of its shiny surface, but also because of its low orbit; it would appear from below one side of the horizon, cross the sky, then disappear below the opposite horizon after crossing the sky, as happens with all LEO satellites. The spacecraft was nicknamed a 'satelloon' by those involved in the project.

Echo 2

Echo 2, a 41.1 m diameter metallized PET film balloon with an improved inflation system to improve the balloon's smoothness and sphericity, was launched January 25, 1964 on a Thor Agena rocket. It was used for more passive communications experiments, and also to investigate the dynamics of large spacecraft and for global geometric geodesy. NASA abandoned passive communications systems in favor of active satellites following Echo 2. Echo 2 reentered on June 7, 1969.

Military use

The Echo satellite program also provided the astronomical reference points required to accurately locate the Russian city of Moscow geographically. This improved accuracy was sought by the US military for the purpose of targeting intercontinental ballistic missiles. [Gray, M. (1992) "Angle of Attack: Harrison Storms and the Race to the Moon". pp 5-6, Pub: W. W. Norton & Co Inc. ISBN 0-393-01892-X.]

ee also

* Project SCORE, the world's first communications satellite, launched in 1958.
* Courier 1B, launched in 1960.
* Telstar, the first active, direct relay communications satellite, launched in 1962.
* AO-51, AMSAT-OSCAR 51 (also known as Phase 2E, or ECHO), an amateur radio communications satellite launched in 2004.
* PAGEOS - a similar balloon satellite project
* Nick D'Alto "The Inflatable Satellite", "Invention and Technology" Summer 2007, Volume 23, Number 1 pp. 38-43.

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