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Space

AIT (Atmospheric Interceptor Technology) EA



APPENDIX B: AIR QUALITY


1. Computation of ait Solid Rocket Motor Atmospheric Emissions and Dispersion

The Joint Army Navy NASA Air Force (JANNAF) Solid Propellant Rocket Motor
Performance Prediction Computer Program (SPP), Version 6.0 was used to determine
exit plane emissions from each ait solid rocket motor. The chemical composition of
each ait stage is given in Table A-1. The industry standard SPP code models performance and chemistry from the combustion chamber to the nozzle exit plane of solid rocket motors. The chemical composition of the exhaust, determined with the
SPP code was input to the Standardized Plume Flowfield Model (SPF3),
Version 3.5, to model the post-exit-plane plume through the region of
mixing and afterburning to several hundred meters downstream (i.e. the
far-field). High temperature reactions which occur in the afterburning
region can convert exit plane species to other compounds. For example, HCl
is converted to Cl and Cl2 in this region of the plume. NOx can also be
produced in this region from the entrainment of ambient atmospheric species
under plume conditions. The extent of afterburning, and thus conversion of
species decreases with increasing altitude and eventually shuts down.


The ait flight vehicle is comprised of modified versions of the 2nd and 3rd
stages of the Minuteman II missile. The model calculations were performed
using specifications of the Minuteman II motors (nozzle geometries,
operating conditions, propellant compositions, and propellant mass flows)
except that the nozzle of the ait 1st stage motor (SR-19 Minuteman 2nd
stage motor derivative) was taken to have an area expansion ratio of 10:1.
The model for the ait 2nd stage engine (the M57 Minuteman 3rd stage)
employed a single equivalent nozzle for the actual cluster of four nozzles.


Altitudes from the ground up to 40 km were considered (i.e. up through the
troposphere and stratosphere). At each altitude, the SPF3 plume model was
run for the average thrust level of the appropriate motor (i.e.
approximately 52,000 and 18,000 lbf for the 1st and 2nd stage motors
respectively) to a distance downstream where afterburning ceased. At that
point, the mass flows of relevant species were determined by integrating
over a plane perpendicular to the plume axis. The mass flow of each species
was then divided by the total mass flow from the motor at the nozzle exit
plane. The resulting ratio is the species mass deposition rate relative to
the total exit-plane propellant mass flow rate, which in the case of the
1st stage motor is 205 lbm/s at average thrust and in the case of the 2nd
stage engine is 65 lbm/s at average thrust. The fractional mass flow for
individual species are multiplied by the total mass flow rate to obtain
quantities of any species emitted by the nozzle.


The thrust (and mass flow rate) for a solid-fuel rocket motor can be
significantly time dependent, varying by as much as +- 20% over the course
of the main burn. The modeled relative mass deposition rates, however are
not expected to be a strong function of thrust over typical excursions.




1.1 Stratospheric Emissions

The output of the SPF3 Version 3.5 code was used to determine stratospheric emissions. For the 15 to 40 km altitude region of the stratosphere, quantities of
substances deposited (HCl, Cl2, Cl, Al2O3 and NOx) were calculated by
integrating the quantity of each species deposited (mass fraction x total
mass deposited) over time.

1.2 Ground-Level Emissions and Dispersion

Computer model calculations have been performed to estimate the hazardous
chemical concentrations in the air after both normal launches and ground
level aborts of the ait vehicle from the Kodiak Launch Complex. The primary
model used for these calculations is REEDM (Rocket Exhaust and Effluent
Diffusion Model) Version 7.07 (Ref. 6). This model is designed to take into
account the fuel and oxidant load, as well as the local meteorology and
terrain to predict pollutant concentrations as a function of time and
distance after a launch event. The REEDM uses a chemical thermodynamic
program (NASA Lewis Chemical Equilibrium CET 89) to estimate such
quantities as peak temperature and cloud rise following an abort. For a
normal launch, output data from the SPP and SPF3 models on the heat content
and chemical composition of a motor plume are input into REEDM.


REEDM was developed originally in 1982 by the H.E. Cramer Company, Inc.; it
was based on multilayer dispersion models developed at the NASA Marshall
Space Flight Center, and originally intended for the Space Shuttle. It has
been used by the Air Force for applications involving Delta, Atlas and
Titan launches in the intervening years. REEDM is used by range safety
officers as the basis of launch/no-launch determinations at CCAS and VAFB.
Several versions have been developed; Version 7.07, used here, was
developed by ACTA Inc., in 1995. The REEDM calculations provided here were
performed by The Aerospace Corporation, El Segundo, CA.


In order to use REEDM for the current problem, a database needed to be
developed for KLC and the ait vehicle. The previous EA for the Kodiak
Launch Complex, indicated that the terrain feature having the greatest
impact on dispersion is a mountain 610 m high, 5 km east of the launch
site. This terrain data base used a 10 degree slope and assumed the
remaining terrain was flat.


Figures 1-9 show the results of the REEDM predictions for nominal and abort situations for two meteorological cases and two launch dates. For the launch dates scheduled in March and in July, the winds used (from NOAA data for Kodiak) were 5.5 m/s and 3.45 m/s respectively, while the temperatures were 0.5 C and 12.4 C, respectively. A worst case wind, which is nearly calm out of the west was also
characterized. An average of 1.75 m/s for the nearly calm winds was used.
The worst case occurs 2% of the time throughout the year. The REEDM
calculations indicate that HCl, Cl2, CO, NO and Al2O3 are species of
potential concern from the ait vehicles. However as shown in Fig. 1-9, the
peak concentrations and worst case 60 minute exposures for each of these
species is far below applicable human exposure standards. These are
discussed in Section 4.8 of the ait Environmental Assessment.


 
 

REFERENCES


1. Burke, M. L. and Zittel, P. F., "Laboratory generation of free chlorine
from HCl under stratospheric afterburning conditions", Combustion and
Flame, in press, 1997.


2. Zittel, P. F., "Computer model predictions of the local effects of large
solid fuel rocket motors on stratospheric ozone", The Aerospace
Corporation, El Segundo, CA, TR-94(4231)-9, 1994.


3. Brady, B.B., et al., "Stratospheric ozone reactive chemicals generated
by space launches worldwide", The Aerospace Corporation, El Segundo, CA,
TR-94(4231)-6, 1994.


4. Jackman, C. H. et al., "Space Shuttle's Impact on the Stratosphere: an
update", J. Geophys. Res., Vol. 101, 12523-12529 (1996).


5. Beiting, E.J., "Solid Rocket Motor Exhaust Model for Alumina Particles
in the Stratosphere", J. Spacecraft and Rockets, Vol. 34, 303-310,
May-June, 1997.


6. J. R. Bjorklund, "User's Manual for the REEDM Version 7 Computer
Program, TR-90-157-01, April 1990, H. E. Cramer Company, Inc., Salt Lake
City, UT and Randolph L. Nyman, REEDM Version 7.07 Prototype Software
Description, TR-950314/69-02, September 1995, ACTA, Inc., Torrance, CA.


7. B. B. Brady, "Modeling the Multiphase Atmospheric Chemistry of Launch
Clouds," Journal of Spacecraft and Rockets", Vol. 34 (5), Sept. - Oct.,
1997.










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