PAGEOS

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PAGEOS (PAssive GEOdetic Satellite) was a balloon satellite which was launched by the NASA in June 1966. Pageos had a diameter of 31 m (thin polyester foil plus a reflecting layer) and was used for the Weltnetz der Satellitentriangulation (Worldwide Satellite Triangulation Network) -- a global cooperation organized by Hellmut Schmid (Switzerland & USA) 1969-1973.

Finished in 1974, the network connected 46 stations (3000 - 5000 km distance) of all continents with an accuracy of 3-5 m (approx. 20 times better than terrestrial triangulations at that time).

The PAGEOS orbit was a polar one (inclination 85-86°) with a height of approx. 4000 km, sinking down gently up to 1975. The reentry occurred in July 1975, closing one of the most successful satellite projects of the 20th century.

Pageos' predecessors in satellite triangulation were the balloons Echo 1 (1960, 30 m) and Echo 2 (1964, 40 m) which were used for passive telecommunication, too. Their visual magnitude was 1 mag, that of Pageos 2mag (like Polaris) due to its higher orbit. Pageos could therefore be observed simultaneously e.g. from Europe and America. PAGEOS appeared as a slow-moving star (at first glance it would appear to be stationary). Its orbital period was approximately three hours. Because of its high orbit and polar inclination it could avoid the earth's shadow and be observed any time of the night (low-orbit satellites are only observable shortly after sunset and before sunrise). In the early 1970s PAGEOS varied from 2nd magnitude to beyond visibility over a period of a few minutes, possibly due to partial deflation and rotation.

See also: Stellar triangulation, Echo satellites, global reference ellipsoid, WGS84