NASA Crew Exploration Vehicle and Launch Abort Tower Aerodynamic Separation Characteristics

Abstract

The subsonic aerodynamic characteristics of the NASA Crew Exploration Vehicle (CEV) and Launch Abort Tower (LAT) were investigated at 0.2 Mach with a focus on the separation effects of the two units at different distances and offset angles. Safety of flight and stability of the CEV/LAT system requires knowledge of the effect of the offset angle and separation on the forces and moments acting on both the CEV and LAT while in close proximity to each other. The CEV/LAT model was tested at five different offset angles and three distances aft with a negative angle of attack sweep in the U.S. Air Force Academy Subsonic Wind Tunnel. Lift, drag, and pitching moment coefficients were analyzed and compared to CEV and LAT alone characteristics. For this evaluation, results for the CEV indicated, that as angle of attack became more negative, the lift coefficient increased, the drag coefficient decreased, and pitching moment coefficient increased, maintaining static longitudinal stability. Lift and drag coefficients of the CEV also increased with increasing offset angles for all angles of attack. Results showed the CEV to be longitudinally unstable when changing the offset angle at 2” and 4” aft, which could pose a safety of flight risk. Results for the LAT showed, as angle of attack becomes more negative, lift coefficient increased, drag coefficient remained constant with no offset, and pitching moment coefficient decreased at 4” aft, and increased at 0” and 2” aft. Increasing offset angles on the CEV created an increase in lift and drag coefficients on the LAT. Results also showed a drastic decrease in drag on the CEV and significant increase in drag on the LAT for the 0 inches aft condition. With combined results of the CEV and LAT tests, there is a significant concern that, due to each unit’s aerodynamic characteristics, the CEV and LAT will be drawn toward each other throughout the separation phase. Analysis using Computational Fluid Dynamics (CFD) is suggested to further explain these experimental results. The effort was sponsored by NASA Johnson Space Center (JSC).