13. 0 ENVIRONMENTAL EFFECTS ASSESSMENT There are profound mutual effects envisioned between SPS elements and the respective environment in which interactions would take place. The analysis, testing, and definition of resulting impacts on the SPS systems design are a major topic of present and future efforts. A summary review of SPS environmental interactions covers the range from Earth surface to geosynchronous orbit. For convenience this range can be divided into the terrestrial environment (Earth surface through strato- phere) and the space environment (ionosphere, thermosphere, magnetosphere, and the geosynchronous distance). The general approach toward assessing the multitude of interactions between SPS program elements and the various environments is through careful analytical modeling of environmental parameters and the introduction of the applicable program elements. The resulting interactions will be evaluated against acceptable tolerance limits and introduced into the overall SPS systems definition efforts as design guidelines and constraints. The definition of acceptability will have to rely on various political processes. Certain environmental interactions that are of fundamental importance and that possibly create global consequences will have first priority. These are listed in Table 13-1. A summary of the major areas of potential SPS environmental interactions is given in Figure 13-1. A special discussion on the SPS collision probability with other satellites and possible effects on maintenance activities is given in subsection 7.1. 7.1. Tasks are being initiated in the following areas: • Definition of the environment at geosynchronous orbit • Definition of the physical processes that cause spacecraft charging and investigation of sheath perturbations around high altitude spacecraft • Quasi-static modeling of the environment interacting with SPS including effects such as: — Differential charging — Variable geometry
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