The plan for phase 2 is being refined in light of the output from the four workshops mentioned above plus additional solicited comments from other interested groups. In view of the short time available to complete the preliminary environmental assessment (less than 1.5 years), it is not likely that major new research programs can produce significant results before FY 80. Consequently, essential new information will have to be acquired through processing and analysis of existing data, theoretical calculations using existing or slightly refined computer models, and taking advantage of already planned experiments (e.g., rocket launches) that could yield useful information. It is recognized, of course, that after 1980 the space shuttle program will present many new opportunities for improving our understanding of the natural and perturbed atmosphere and for verifying current predictions of atmospheric effects and their subsequent impacts on the environment. For example, plans are already in progress to conduct ionospheric depletion* experiments that require special burns of the space shuttle rocket engines over locations on the ground where ionospheric observations are located. The exhaust products of these burns are expected to remove large numbers of electron-ion pairs from a region of the upper atmosphere called the F2 layer of the ionosphere. Instrumentation located at the observatories will be used to study the nature and extent of these ionospheric depletions. Similar experiments are discussed more fully in Section 3.4.1. 3.3 CAUSE AND EFFECT RELATIONSHIPS The cause and effect relationships that may play a significant role in determining the impact on the environment are in most cases not well-defined at this time. Those that are defined herein should be regarded as being not only preliminary in nature but also rather speculative. Figure 3.3 illustrates causes or disturbances and their potential immediate, intermediate and subsequent effects. 3.4 STATE OF KNOWLEDGE 3.4.1 Upper Atmosphere, Nonmicrowave Effects (above 60 km) The state of knowledge regarding most of the cause and effect relationships indicated in Section 3.3 is not sufficiently advanced at this time to *Removal of electron-ion pairs.
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