[4] The orbit of the HLLV is inclined 45° to the equator. [5] The end point of the entry flight defined as the point where the altitude is 50 km is latitude 40 °N and longitude 120 °W, so that the craft could land on an airfield in central California. [6] The atmosphere rotates with Earth without any slip. The entry trajectory can be varied by varying [1] the duration of the retrorocket bum at the orbit (the amount of fuel required for this purpose would be very small, and so its mass is ignored), [2] the lift coefficient (i.e., flap angle), [3] the initial angle of attack, [4] the final angle of attack, |5] the altitude at which the angle of attack begins to decrease, and [6] the rate at which the angle of attack is changed. In the present work, these variable parameters were changed over a wide range in order to generate a family of possible entry trajectories that satisfies the condition of maximum allowed deceleration of 1.4 g. The calculation requires a straightforward numerical integration of the Newtonian equations of motion in two dimensions. Earth was assumed to be a perfect sphere, and the atmospheric data of the U.S. Standard Atmosphere (27) were used for the calculation. Figure 4 shows the profiles of such flight trajectories. As indicated, the trajectories are produced by varying retro-AV, that is, the velocity decrement achieved by firing the retrorockets, between -0.105 and -0.110 km/sec (-344 and -360 ft/sec). At the altitude of 120 km (75 mi), these two AV values produce entry velocities of 7.588 and 7.583 km/sec (4.715 and 4.712 mi/sec), and entry angles of -0.896° and -1.103°, respectively. Of these, three typical trajectories were selected for computation of the NOj. production rate. According to the distance required for the entry flight to end, they are referred to here as “shallow,” “nominal,” and “steep” trajectories, as shown. The rate of NOZ production along these trajectories was calculated by the method of Park (28). In brief, the method assumes that the amounts of NO^ produced by a spacecraft are the same as that produced by a circular cone having the same overall chord length, overall surface area, and angle of attack. Such a method is shown (28) to yield approximately the same amount of NO^as a real spacecraft with a blunt nose, at least up to the point where such an “exact” calculation was possible. The computer code used by Park (28) was run in the present study. The code calculates
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