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APPENDIX N

IMPACT OF EARTH LAUNCH VEHICLES ON THE OZONE LAYER

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:

Cl+03 -> C10+02

CIO+O -> C1+02

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)

TABLE 4-18.- ANTICIPATED LAUNCH RATES IN LAUNCHES PER YEAR*

Year from
startof
colonization
program
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 Max. Total
HLLV
(150 t/launch)
- - - - 9 26 23 53 54 71 65 49 53 65 69 76 72 72 67 73 73 73 76 1043
Space Shuttle
(30 people/launch)
- - - - 13 13 13 20 17 27 27 100 100 100 83 83 83 83 80 80 80 80 100 1082
TOTAL - - - - 22 39 36 73 71 98 82 149 153 165 152 159 155 155 147 153 153 153 165 2125
*No provision for launching propellant is included in these numbers; its inclusion will more than double the annual launch requirements.

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:

O(1D) + H20 -> 20H

in which the O(1D) results from ozone photolysis at wavelengths shorter than 310 nm. The OH reacts with add oxygen in a catalytic cycle
OH + 03 -> HO2 + O2
HO2 + O -> OH + O2

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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