Hydrogen chloride gas (HC1) produced from the exhaust of the Space Shuttle booster motor (see fig. 4-29) dissociates to produce free chlorine which, in turn, reacts to remove ozone from the stratosphere by the following catalytic reactions:
One-dimensional models of HC1 deposition, vertical transport, and chemical production and removal of participating trace stratospheric constituents (OH, O, O(l D), 03 , CH4, H2, and NO) have been used by NASA to simulate ozone depletion (refs. 45, 46). Steady-state solutions were obtained simulating 60 shuttle launches per year given that the emissions were spread uniformly in the horizontal over a hemisphere and over a 1000-km wide zone. The levels of ozone reduction computed were about 0.3 percent and 1.0 percent, respectively. More recently, Whitten has revised the ozone depletion calculation for the hemisphere downward to less than 0.1 percent (personal communication, July 1975). Launch rates that might be anticipated for the initial colonization program are shown in table 4-18.
TABLE 4-18 (gif format)
The reduction in ozone concentration in the upper levels of the atmosphere allows the molecular oxygen dissociating radiation to penetrate lower before producing ozone; hence, a primary effect is a downward shift in the ozone distribution. A reduction in the total ozone concentration, which would appear to be very minor, results only as a secondary effect
Advanced launch vehicles using liquid oxygen-liquid hydrogen (LOX-LH 2) propellants above 30 km would eliminate the emission of hydrogen chloride into the stratosphere; however, there are also potential problems with hydrogen fuel which produces water. Water is dissociated as:
However, compared to the 2 ppm of water in the stratosphere, increases due to hydrogen combustion may be negligible. Further study of the problem is required (R. Whitten, NASA Ames Research Center, personal communication, August 1975).
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