3. CALCULATION OF NOX PRODUCTION DURING HLLV REENTRY The average mass of the HLLV at reentry is 452.6 tonnes (499 tons) (25). The total projected area of the craft is determined from the figures in Ref. 25 as approximately 2280 m2 (24,530 ft2); the initial orbit height of the craft is given as 450 km (280 mi). Reference 25 also specifies that the deceleration of the HLLV during reentry shall be less than 1.4 g. The report does not specify, however, the reentry flight trajectory or the lift and drag characteristics of the gliding body needed in a trajectory calculation. Presumably, such aerodynamic data have not yet been generated. In order to estimate the amounts and spatial distributions of NOX produced during the reentry flight, therefore, the following assumptions have been made. [1] The functional relationship between the drag coefficient and the angle of attack of the craft is the same as for the Space Shuttle Orbiter, as given in the design report (26). [2] The lift coefficients of the vehicle are expressible as a product of the lift coefficient values of the Space Shuttle Orbiter given by Ref. 26 and an arbitrary fixed constant not greater than unity. Controlling lift coefficients in this manner would be possible, for instance, by varying the angle of wing flap. [3] The angle of attack remains fixed at a high value initially. When the craft reaches a certain intermediate altitude [of about 70 to 80 km (43-50 mi)], the angle of attack is changed at a steady rate to a low value.
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