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ESA's Geos-1 satellite is being prepared for launch in the Netherlands

The GEOS ( Geostationary Earth Orbit Satellite ) program of the European Space Agency included the first satellites in geostationary orbit that were used exclusively for scientific purposes. In the parlance of NASA , which was responsible for the launch of the satellites, these satellites are also referred to as ESA-GEOS in order to distinguish them from the NASA GEOS program of the same name .

The task of the satellites was to measure the electric and magnetic fields , the plasma - magnetic field interactions and the energy and angular distribution of the charged particles ( electrons and ions ) in the geostationary orbit .

The satellites had a cylindrical design with a height of 1.32 m. Without fuel, they each weighed 274 kg. In orbit they unfolded four 2.5 m long booms, two 20 m long cable booms and two 3 m long lockable booms for the various sensors. To prevent electrostatic charges , 96% of the satellite surface was electrically conductive.

Both satellites were identical, apart from minor modifications to some experiments.

Satellites in the GEOS program

  • GEOS 1 (before launch, GEOS A) was launched from Cape Canaveral on April 20, 1977 with a Delta-2914 rocket. A failure of the Delta rocket means that the geostationary orbit could not be reached. Some of the experiments could also be carried out from the highly elliptical orbit with a 12-hour orbit, between 2682 and 38,475 km altitude at a 26.6 ° orbit inclination.
  • GEOS 2 (before launch, GEOS B) was successfully launched from Cape Canaveral on July 14, 1978 with a Delta-2914 rocket and then positioned at 37 ° East above the equator.


  1. a b ESA Achievements, BR-200, November 2001 ( Memento from July 11, 2004 in the Internet Archive )

Web links

Commons : Geostationary Earth Orbit Satellite  - collection of images, videos and audio files