spase://SMWG/Observatory/Equator-S

Equator-S is an element of the International Solar-Terrestrial Physics (ISTP) program. Spacecraft design, manufacturing and
testing were provided by the Max-Planck-Institut fur Extraterrestrische Physik (MPE). The project was financially supported by DARA
(Deutsche Agentur fur Raumfahrt Angelegenheiten). Some assistance and in-kind contributions were received from ESA/ESTEC and NASA.
Mission analysis and operations are the responsibility of the German Space Operations Center (GSOC) of the DLR. The spacecraft was
launched December 2, 1997, as a secondary payload on an Ariane IV vehicle from Kourou (French Guiana). Equator-S is different from
NASA's ISTP/EQUATOR spacecraft, which was dropped when the ISTP mission was re-scoped in late 1989.

The Equator-S objectives are to
provide high-resolution plasma, magnetic, and electric field measurements in several regions not adequately covered by the existing
ISTP missions, namely the low-latitude dayside magnetopause and its boundary layer, the equatorial ring current region, and the near-earth
equatorial plasma sheet. These regions play key roles for our understanding of the global perspective of solar-terrestrial relations as
well as the detailed plasmaphysical processes.

The orbit is near-equatorial, with 500 km perigee altitude and 11 Re geocentric apogee
distance. The payload consists of seven scientific instruments provided by international groups to study the solar wind and charged
particles trapped in the earth's magnetosphere. For reasons of cost and schedule, these instruments are largely derived from engineering
or spare units from other ISTP missions. Innovative sub-systems for solar power and orbit measurement are tested on Equator-S for the
benefit of future spacecraft designs. Furthermore, some technological experiments have been added that exploit the hard radiation
environment of the Equator-S orbit or make use of its orbital features. These include a GaAs solar cell to check on temperature and
I/V - characteristics, and degradation by radiation; and a GPS receiver to study the GPS capabilities as a function of spacecraft
altitude. There is also a mass memory of 192 MBytes of CMOS RAM for temporary data storage.

    The rapid spacecraft spin rate (60 rpm) allows unprecedented high temporal resolution of the measurements. At the regular telemetry
    contact with the Weilheim ground-station on 1 May 1998, EQUATOR-S stopped sending data, although the TM-signal was unchanged.
    This is attributed to a failure of the redundant processor, similar to the failure of the first processor on 17 December 1997.
    All attempts to command the spacecraft failed. However, GSOC will continue this effort. If a latch-up caused by penetrating particle
    radiation was the cause of the failure, there is hope that it may heal itself upon the next eclipse (August 1998) because of the complete
    temporary switch-off of the electrical system.