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We developed a variable-output-aperture, laboratory plasma source to enable real-time plasma density control with minimal effect on other plasma properties. The source is capable of producing a low-Earth-orbit-type plasma with electron energies of approximately 0.1–0.7 eV and streaming ion energies of approximately 2–4 eV. The plasma density can be adjusted over two orders of magnitude, thus representing some of the natural variability of the ionosphere. In a given aperture range, the electron and ion density decreased by 73% while the average percent difference in electron and ion density was 0.3% with a standard deviation of 1.4%. The average percent difference in ion energy was 6.3% with a standard deviation of 4.3%. The variable aperture was achieved by a rotating dual-grid system. [ABSTRACT FROM AUTHOR]

We present an analysis of the charging interactivity between surrounding surface materials aboard a spacecraft at geosynchronous altitudes. In particular, bootstrap charging of a small surface may occur if is surrounded by a large negatively charged surface. Here, a negative potential barrier forms above the small surface, resulting in suppression of photo- and secondary electron emission from that surface. Additionally, the small sur- face experiences an enhancement of the collection of the photo- and secondary electrons emitted from the surrounding surface. This mechanism results in the charging of the small surface to higher levels than that of the patch in isolation, and in many cases the final potential will reach that of the potential of the larger surrounding surface. With this study we examine bootstrap charging behavior with model data and with data collected on orbit. We have modeled the DSCS-III B7 geosynchronous satellite with realistic geometry and spacecraft materials. Additionally, a previous study has shown that bootstrap charging has been observed on the DSCS-III B7 geosynchronous spacecraft. Both Astroquartz and Kapton cloth patches charged up to the frame potential of the satellite during periods of severe frame charging. The results of modeling bootstrap charging of a small Kapton patch floating relative to the DSCS-HI frame fixed at a potential of -1,000 V show that the patch will indeed charge up negatively to match the frame potential, with the temporal increase in negative potential following an exponential time characteristic. [ABSTRACT FROM AUTHOR]