11/1/93: NASA STATEMENT CONCERNING SPACE SHUTTLE SRB EXHAUST EFFECTS ON OZONE 

Scientific information on the effects on ozone of chlorine exhaust from the
Space Shuttle's Solid Rocket Boosters is contained the 1990 Report to Congress
from NASA's Upper Atmosphere Research Program. Using a launch scenario of nine
Shuttle launches and six Titan IV launches per year, model calculations
examined the spread of the exhaust plume from a single Shuttle launch and then
followed the steady-state buildup of chlorine from several years of launches.

The report found that the chlorine released annually in the stratosphere by the
projected Shuttle launches is about 0.25 percent of the total amount of
halocarbons released during a year on a global basis (0.725 kilotons by the
Shuttle; 300 kilotons from all sources).

The report concludes that Space Shuttle launches at the current rate pose no
significant threat to the ozone layer and will have no lasting effect on the
atmosphere.  The exhaust plume from the Shuttle represents a trivial fraction
of the stratosphere, and even if ozone destruction occurred within the initial
plume, its global impact would be inconsequential.  Further, the corridor of
exhaust gases spreads over a lateral extent of greater than 1,000 kilometers in
a day (approximately 600 miles) and thus no local "ozone hole" could occur
above the launch site.

Images taken by the Total Ozone Mapping Spectrometer (TOMS) aboard NASA's
Nimbus-7 satellite at different points following shuttle launches show no
measurable ozone decrease.

Copies of the Congressional Report, An Assessment of the Impact on
Stratospheric Chemistry and Ozone Caused by the Launch of the Space Shuttle and
Titan IV, are available from the following source:

NASA Headquarters Newsroom 
300 E. Street, S.W.
Washington, D.C.  20546
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  Via FTL BBS (404-292-8761) and NASA Spacelink (205-895-0028)
