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An analysis of differential charging between dielectric surface materials and the frame of a DSCS-III geosynchronous spacecraft is presented. Charging levels measured by surface potential monitors (SPMs) covered with samples of Kapton and Astroquartz have been recorded for one half of a solar cycle. Both seasonal and solar cycle effects are seen in the daily peak levels of the SPM voltages, with local maxima occurring near the equinoxes and a general trend increasing as solar max is approached. Charge neutralization by an onboard Xe plasma contactor was demonstrated to be effective throughout the mission, with a mean voltage reduction of 86% for Astroquartz and 74% for Kapton. Though a statistical analysis shows a general correlation between the fluence of charging electrons with SPM voltages, the event-specific correlation contains enough variance to cast doubt on the usefulness of an electron sensor as a differential charging alarm. We have found that a Kapton-covered SPM may be better suited than an electron sensor as a differential charging alarm. Index Terms--Geosynchronous orbit, satellite charging, space environmental effects, space weather.

This paper discusses the connection between changes in Earth''s thermosphere and ionosphere induced by changes in the Earth''s local space environment (or “space weather”) and the phenomena observed in far ultraviolet images of the Earth. Two new experiments, the Global Ultraviolet Imager (GUVI) and the Special Sensor Ultraviolet Imager (SSUSI), will provide a new capability for monitoring changes in thermospheric composition and ionospheric density as they change in response to space weather. These sensors provide a ten-fold improvement in spatial and temporal resolution and a greater than ten-fold improvement in sensitivity over that provided by sensors on the POLAR and IMAGE satellites. These sensors are expected to provide new insights into the mesoscale coupling between the ionosphere and thermosphere, as well as allowing us to develop a better specification of the high latitude convection electric field pattern. [Copyright &y& Elsevier]