EQUATOR-S is a low-cost mission designed to study the Earth's equatorial
magnetosphere out to distances of 67000 km and it forms an element of the
closely-coordinated fleet of satellites that
... comprise the IASTP program
(http://www-istp.gsfc.nasa.gov/istp/sci_operations/www-sites.html) . It is
based on a simple spacecraft design and carries a science payload consisting of
advanced instruments that were developed for other IASTP missions. Unique
features of EQUATOR-S are its nearly equatorial orbit and its high spin rate.
It was launched as an auxiliary payload on an Ariane-4 on December 2nd, 1997.
The mission is intended for a two-year lifetime.
The idea of an equatorial satellite dates back to NASA's GGS (Global Geospace
Science) program originally conceived in 1980. When the equatorial element of
the program was abandoned in 1986 and several subsequent attempts to rescue the
mission had failed, the Max-Planck-Institut f?r extraterrestrische Physik (MPE)
decided in 1991 to fill this gap in the GGS (and in the international IASTP)
program because of its interest in the global magnetospheric science, and
because it provided an opportunity for a test of an advanced instrument, EDI,
to measure electric fields with dual electron beams. The realization of
EQUATOR-S was possible through a grant from the German Space Agency DARA
(meanwhile part of DLR), that was approved in late 1994, but also through
MPE-internal funds and personnel.
For more information, see:
http://www.mpe-garching.mpg.de/EQS/eq-s-spacecraft.html 
