charge transfer or ion-molecule reaction to ^0^ or OH”*”, wh^ch Recombine very rapidly with free electrons by dissociative recombination;10 -10J times faster than do atomic 0+ ions. In this way an "ionospheric hole" is created and has been observed previously, in particular after the launch of Skylab-I (Mendillo et al., 1975a, b). Preliminary calculations for a single HLLV second stage burn indicate a 40-50% electron density depletion in the F-region at night, with negligible depletion by day, and a 3-4 day recovery time. These effects are limited to altitudes above which the air ions are atomic, roughly 160-180 km; at lower altitudes the water/hydrogen injections will have a far smaller and more subtle effect (see Zinn et al., 1978, 1979; Mendillo et al., 1979). Zinn et al. (1979) have made a fairly detailed comparison with the Skylab observations, and find reasonable agreement with the Sagamore H111-ATS3 observations for appropriate values of the various parameters, in particular ionospheric winds, since their calculations indicate that the ionized hole disappears because it is blown out of the line of sight rather than because of re-ionization. Clearly these single injection calculations do not tell us all that we need to know about the multiple launches associated with SPS construction, and this problem is discussed next. 3.2.2 Ionospheric Depletion due to the Multiple Launches during SPS Construction As a result of the frequent (almost daily) launches associated with SPS construction operations one would expect to find a large region of constantly depleted ionization located near the launch site, which presumably would be Kennedy Space Center (Lat. 28.5°N, Long. 80.5°W). The largest effect will be due to the low altitude (70-120 km) burn of the HLLV second stage, and in particular due to H2 rather than to H2O emissions. At the altitudes of injection the H2 is not photodissociated rapidly, but is oxidized slowly to water. However, it mostly diffuses upward into regions where there are large concentrations of 0-atoms and a higher temperature, so that the oxidation to H2O becomes rapid. In this way the HLLV gives rise to a relatively large concentration of ^0 in the atmosphere above 120-150 km where there is normally very little water. (By contrast, the injection of ^0 due to the HLLV second stage is probably not as important: it is not photodissociated but goes into a region in which there are significant quantities of water already, and it tends to freeze out and fall down. It cannot diffuse upward as rapidly as H2 can, and thus is unlikely to affect the ionospheric F-region to the same extent.) The effective de-ionization chemistry is somewhat complex; see Zinn et al. (1979) for an overall discussion, and Section 3.2.3 for details of the dissociative recombination of H20+ and 0H+. Overall, one may expect a region of reduced ionization at altitudes above 160-180 km (at lower altitudes most ions in the normal ionosphere are molecular N0+ and 02+, which recombine quite fast with electrons, so that the addition of ^0 is unlikely to produce a very large effect), and up to several
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