PAGEOS was a balloon satellite

Balloon satellite

A balloon satellite is a satellite that is inflated with gas after it has been put into orbit.-List of Balloon Satellites:...

 which was launched by the NASA

NASA

The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 in June 1966. Pageos had a diameter of exactly 100 feet (30.5 m), consisted of a 0.5 mil thick mylar plastic film coated with vapour deposited aluminium enclosing a volume of 524000 cubic feet (14,838 m³) and was used for the Weltnetz der Satellitentriangulation (Worldwide Satellite Triangulation

Triangulation

In trigonometry and geometry, triangulation is the process of determining the location of a point by measuring angles to it from known points at either end of a fixed baseline, rather than measuring distances to the point directly...

 Network) -- a global cooperation organized by Hellmut Schmid

Hellmut Schmid

Hellmut H. Schmid was Professor of geodesy and photogrammetry on the ETH Zürich , where he emerited in 1985. In the 1950s, he worked on research projects of space exploration in the USA...

 (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

Inclination

Inclination in general is the angle between a reference plane and another plane or axis of direction.-Orbits:The inclination is one of the six orbital parameters describing the shape and orientation of a celestial orbit...

 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

Telecommunication

Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...

, too. Their apparent magnitude

Apparent magnitude

The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 (brightness) was 1 mag, that of Pageos 2mag (like Polaris

Polaris

Polaris |Alpha]] Ursae Minoris, commonly North Star or Pole Star, also Lodestar) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole, making it the current northern pole star....

) 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

Apparent magnitude

The apparent magnitude of a celestial body is a measure of its brightness as seen by an observer on Earth, adjusted to the value it would have in the absence of the atmosphere...

 to beyond visibility over a period of a few minutes.

External links

• NASA technical note: The fabrication and testing of PAGEOS I

See also

• Stellar triangulation
  Stellar triangulation
  Stellar triangulation is a method of geodesy which uses cosmic instead of terrestrial targets. It was first done by the Finnish geodesist Väisälä in 1959, who made astrometric photographs of the sky at two stations together with a balloon probe between them....
  
  
• Project Echo
• global reference ellipsoid
  Reference ellipsoid
  In geodesy, a reference ellipsoid is a mathematically-defined surface that approximates the geoid, the truer figure of the Earth, or other planetary body....
  
  
• World Geodetic System
  World Geodetic System
  The World Geodetic System is a standard for use in cartography, geodesy, and navigation. It comprises a standard coordinate frame for the Earth, a standard spheroidal reference surface for raw altitude data, and a gravitational equipotential surface that defines the nominal sea level.The latest...
  
  (WGS84)