further analysis, which we intend to pursue in FY81. In general, co-ordination with BUARO proved to be most fruitful in terms of what to look for in future experiments which more closely approximate the SPS scenario, and in terms of theoretical development on ion beam-plasma instabilities. Observations of spacecraft charging during injections of "keV" electrons on the nightside at geosynchronous orbit by the SCATHA satellite impacts the SPS in a way not necessarily involving the external environment where other systems operate. Rather, it impacts SPS operations (involving humans and remote control systems) in the immediate environment of the spacecraft. Therefore, we have kept in close co-ordination with SCATHA experimenters throughout FY79 and FY80. Since SCATHA was launched in 1978, data analysis is not yet complete, so analysis in terms of possible SPS impact is presently premature. However, from what is demonstrated in observations of selected spacecraft charging events, it appears that SCATHA results fully demonstrate the effects of the spacecraft upon its immediate particle and fields environment. We intend to continue co-ordination with SCATHA. In FY80, considerable co-ordination activity was devoted to configuring an active ion engine experiment with a space shuttle facility which is of sufficient magnitude to bridge the gap between present observational results and the SPS scenario. As the result of a number of contacts during FY80, we are attempting to put together a shuttle experiment under the auspices of the DOE, NASA and the USAF. Initial indications from all three agencies seem to be positive insofar as the general conception and commonality of interests are concerned. Further, it was noted that field emission ion engines developed at the European Space Technology Center (ESTEC) have specific impulses quite similar to those projected for the SPS, although these European ion engines have not been tested in space. Co-ordination activity to configure and to 73
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