Nasa's pioneering satellite, Echo 1, celebrates its 50th anniversary at the peak of this year's best meteor shower
* Alan Pickup
* guardian.co.uk, Wednesday 4 August 2010 08.00 BST
* Article history
Echo 1, the pioneering communications satellite. Photograph: Nasa Photograph: Nasa
The peak of the year's best meteor shower, the Perseids, on 12 August coincides with the 50th anniversary of the launch of Nasa's Echo 1, the pioneering communications satellite that was a conspicuous addition to our night sky during the 1960s. Consisting of a Mylar balloon 30.5 metres in diameter, Echo 1 orbited initially at a height near 1,600km, and was used like a giant mirror to reflect radio signals between two points on the Earth's surface.
As such it was a passive communications satellite; later active ones, such as Telstar that followed two years later, have receivers and transmitters to amplify and relay, or broadcast, the signals. Most of these are now placed in geostationary orbits 35,786km above the equator, where they remain fixed in the sky relative to someone on the ground.
Echo 1 was followed by the larger (41.1 metres) Echo 2 in 1964 before interest in passive communications satellites ended. Both Echos shone brightly in the sunlight as they arced across our sky; it is said that Echo 1 was probably seen by more people than any other man-made object in space, while Echo 2 would rival the ISS in brightness were it resurrected today. In fact, being huge and reflective but of low density, both were subject strongly to the pressure of solar radiation, effectively behaving like solar sails. This distorted their orbits, driving their perigees lower where atmospheric drag soon took its toll. Echo 1 re-entered and burnt up in 1968, followed by Echo 2 one year later.
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http://www.guardian.co.uk/science/2010/aug/04/spacewatch-perseids-meteor-shower
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