PAGEOS
PAGEOS (PAssive Geodetic Earth Orbiting Satellite) was a balloon satellite which was launched by the NASA in June 1966. Pageos had a diameter of exactly 100 feet (30.48 m), consisted of a 0.5 mils (12.7 µm) thick mylar plastic film coated with vapour deposited aluminium enclosing a volume of 524,000 cubic feet (14,800 m3) 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. A disintegration occurred in July 1975, closing one of the most successful satellite projects of the 20th century. A second break-up occurred in January 1976 resulting in dozens of fragments. Most of these re-entered during the following decade, but one piece remains in orbit.
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 apparent magnitude (brightness) 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 apparent magnitude to beyond visibility over a period of a few minutes.
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de:PAGEOS
