European GEOS Mission: the Satellites

Geos was designed for geostationary orbit to study the particles, fields and plasmas of the Earth's magnetosphere using seven instruments provided by ten European laboratories. Because of its unique orbit and the sophistication of its payload, Geos was selected as the reference spacecraft for the worldwide 'International Magnetospheric Study'. Unfortunately, Geos-1 was left in a low transfer orbit following launch on 20 April 1977 because of a problem with its US Delta launcher. As a result, the Qualification Model was launched as Geos-2 on 14 July 1978 with an identical payload and successfully reached the planned orbit. In spite of its orbit, Geos-1 made a significant contribution to IMS, and its mission formally ended on 23 June. Geos-2 was highly successful, creating a huge database for magnetospheric studies and plasma research in general.

Science objectives of the European GEOS Mission
   - to advance our knowledge of the dynamics of the magnetosphere, in particular to study the response of the near-Earth environnment to varying conditions in interplanetary space (nominal objective reached with GEOS-2),
    -to study of the dayside sector of the magnetosphere : the plasma bulge and the plasmapause have been investigated in detail.(GEOS-1).

GEOS comprises the following seven experiments:

S-300
AC-magnetic fields up to 30 kHz
DC/AC electric fields and plasma resonances up to 80 kHz
Mutual and self-impedance
CRPE, Issy-les-Moulineuax, France
Space Science Dept., ESA, ESTAC, Holland
Danish Space Research Institute, Lyngby, Denmark
CRPE, Orléans, France

S-302
Thermal plasma up to 500 eV
Mullard Space Science Lab., Dorking, UK

S-303
Composition (1-140 amu) and energy spectra of ions up to 16 keV
University of Bern, Switzerland
Max-Planck-Institut, Garching, Germany

S-310
Pitch-angle distribution of electrons and protons (0.2-20 keV) energy range
Kiruna Geophysical Observatory, Kiruna, Sweden

S-321
Pitch-angle distribution for electrons (20-300 keV) and protons (20 keV-3MeV)
Max-Planck-Institut, Lindau, Germany

S-329
DC electric field
Max-Planck-Institut, Garching, Germany

S-331
DC and ULF magnetif field
CNR, Frascaty, Italy
NASA/GSFC, Greenbelt, Maryland