2. Experimental (laboratory) study of the dissociative recombination of H20+ and 0H+, including the state of excitation of the products (see Section 3.2.3). 3. Experimental (field) study of the dispersion of tracers in the mesosphere at relatively long times after release (see Section 2.6, especially Fig. 3). 4. An overall 3-D/2-D model calculation of the steady-state F-region depletion to quantify the estimates quoted here (which are not based on any very detailed calculations) and also to identify any further critical unknowns. This is not a simple task (see Section 3.2.4 for an indication of the work called for). 5. To verify the adequacy of the model predictions, it is appropriate to analyze previous results (e.g., the Skylab-I and LAGOPEDO observations), to study and observe targets of opportunity such as the Atlas-Centaur launch of HEAO-C in September 1979, and to study any relevant natural phenomena (see the discussion of Section 3.2.5). 5.3 PROBLEMS INVOLVING H20, H2, AND NO (MAINLY, BUT NOT ENTIRELY, IN THE MESOSPHERE AND THERMOSPHERE) 1. Water vapor concentration in the mesosphere. This is very poorly known at present, but various ongoing and planned satellite measurements should produce a great improvement over the next 10 years or so. If the SPS project goes into detailed engineering development, it will be vital for project management to initiate a long-term water vapor monitoring program over at least a 20-25 year period, so that it can later be established whether SPS rocket activity does indeed enhance the level of water vapor in the mesosphere as anticipated. On a short-term basis two action items are: (See Section 2.11.1). 1.1 The development of ground-based microwave techniques. 1.2 The intercomparison of different potentially useful techniques for water vapor measurement. 2. High altitude clouds and contrails. While the expected climatic effects of both high altitude artificial clouds and rocket contrails are small, they are not clearly negligible. Moreover, there are possible effects on remote sensors. Thus, as in the case of water vapor, a long-term data base on noctilucent and nacreous clouds must be developed once SPS engineering development is under way. However, there is another class of problems relating to the physical mechanisms for condensation and evaporation of water for both natural clouds (which may be enhanced by SPS) as well as for any long-lived contrails. These problems are important at the present stage of analysis because the ultimate impact of water injections by rockets depends on its rate of removal from the upper atmosphere, which is much faster for aerosols than for vapor. 3. Fate of injected H20/H2« Theoretical studies are needed to understand all aspects of the water/hydrogen budget of both low-altitude
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