The Orion Multi-Purpose Crew Vehicle (MPCV), NASA's next manned spacecraft, utilizes a staged parachute system during re-entry, which incorporates two drogue chutes in the first stage. At the request of the NASA Johnson Space Center Applied Aeroscience and Computational Fluid Dynamics Branch, Orion drogue chute drag characteristics were evaluated for freestream and in-wake conditions at three distances aft of the Orion MPCV and three different reefing stages by testing a 2.02% scale fabric drogue chute model in free flight in the US Air Force Academy Subsonic Wind Tunnel. This was the first known parachute wake testing at extremely smaU scale. A primary objective was to determine the reduction in drogue chute drag while in the wake of the Orion. However, problems with the test approach became apparent. Initial results indicated that the average drag coefficient in the wake of the Orion model was higher than it was in the corresponding simulated freestream runs. Therefore, the drag deficit of the drogue chutes in the wake of the Orion could not be determined. Several investigations were undertaken to understand why this was the case. Since wild chute dynamics were experienced during free flight testing, the drogue chute model was next tethered to the sides of the wind tunnel with two nylon strings. The results of these tethered runs showed the same trend of the in-wake drag being higher than the freestream drag, indicating that the wild free-flight dynamics may not have been the cause of the inability to determine the drag deficit. Next, a wake pressure survey was performed to determine if the freestream support was producing a more significant wake than the Orion model. It was concluded that the freestream support was not the cause of the inability to determine a drag deficit. A detailed uncertainty analysis was then accomplished which indicated that using fabric parachute models at extremely small scale in free flight is difficult because of relatively high uncertainty. Due to the small scale, inertial and fabric stiffness characteristics were not correct, resulting in chute asymmetry and subsequent dynamic oscillations with increased precision error, making identification of small differences in drag, such as the drag deficit, impossible. Significant recommendations were made to improve future efforts. Despite this inability to quantify the drag loss experienced by the drogue chute, useful data was obtained, including the effect of reefing and the free-flight dynamics of the drogue chute. The 73% reefed chute experienced 38.3% less drag than the fully open chute, and the 54% reefed chute experienced 49.6% less drag than the fully open chute while in the wake of the Orion. In addition, the dynamic response of the drogue chute drag force was determined and showed an overall weak periodic trend, with a dominant frequency of about 126 Hz. The overall experience obtained in this effort should provide a solid foundation for future testing of scaled parachutes.
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