Postflight Apollo command module aerodynamic simulation tests.

Abstract

Initial aerodynamic measurements in the re-entry portion of the unmanned Apollo mission AS-202 trajectory indicated several anomalies between preflight predictions and flight data. Accurate definitions of the trim angle of attack and resulting lift/drag ratio are essential for adequate prediction of splash-down position and to insure that the re-entry aerodynamics of future manned missions can be predicted adequately. A comprehensive wind-tunnel investigation was conducted 1) to simulate the actual vehicle as flown (AS-202) in model construction, 2) to obtain consistent pitch plane force measurements in the angle-of-attack range 150° < a < 180°, 3) to determine the effects of Mach number (from 3 to 20) and Reynolds number, and 4) to evaluate possible sting effects. The investigation indicated that the influence of the ablator (heat shield) geometry prior to ablation causes a significant change in trim angle of attack and a resulting decrease in available lift-to-drag ratio. In addition, a very strong viscous influence exists on the Apollo command module in the initial portion of re-entry extending down to an altitude of about 220,000 ft. The Mach number influence extends up to about Mach 14, which is substantially higher than previous blunt-body investigations have indicated.