Feasibility of Determining Aerodynamic Coefficients for a NASA Apollo Body With the Use of Telemetry Data From Free Flight Range Testing

Report No. ARL-TR-4271
Authors: Benjamin Topper, T. Gordon Brown, Edward Bukowski, Bradford S. Davis, Rex A. Hall, Peter C. Muller, Timothy T. Vong, and Fred J. Brandon
Date/Pages: September 2007; 25 pages
Abstract: The U.S. Army Research Laboratory (ARL) was requested by the National Aeronautics and Space Administrations (NASA's) Langley Research Center to perform a free-flight experiment with telemetry (TM) instrumented sub-scaled re-entry vehicle in order to determine the feasibility of using TM to obtain aerodynamic coefficients. NASA's current ability to collect aerodynamics data of subscale re-entry vehicles has been limited to forced oscillation wind tunnel testing with a sting-mounted model or by free-flight testing in an indoor aeroballistic range. Both testing techniques have shortcomings. The presence of a rear sting and its effect on the capsule's aft-body flow field introduce uncertainties in forced oscillation test results, and aeroballistic testing provides a very limited set of data and relies on the ability to accurately measure small changes in the capsules angle of attack, based on shadowgraph images. The current methods also limit NASA's abilities to test crew exploration vehicle (CEV) geometry variations such as offsetting the center of gravity and non-symmetrical mass distributions. ARL developed and demonstrated a unique experimental technique to capture the flight dynamics of sub-scaled re-entry vehicles while testing on an exterior ballistics range. This technique combines the gun launch of a projectile that uses a double-length 120-mm gun with an instrumentation package contained inside the re-entry vehicle. For the current phase 1 effort being described, a reduced size Apollo (see figure 1) shaped re-entry vehicle was used because of its similarity to the current CEV being proposed and the existence of vast empirical data available to validate this technique. Following muzzle exit, the sabot is discarded and an ARL-developed constellation of inertial and magnetic sensors generate raw data that is telemetered and captured via a ground station. The data are then fed into a custom analysis tool that fuses the various sources, reconstructs the dynamic motion, and extracts the aerodynamic coefficients. ARL has been successfully employing this technique of using free-flight TM data to extract aerodynamics coefficients on numerous current and past Department of Defense munitions programs. Upon successful validation of this technique, NASA foresees employing ARL telemetry technology as an integral tool for its goal to develop an Orion Crew Exploration Vehicle and other re-entry vehicles as part of Project Constellation.
Distribution: Approved for public release
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Last Update / Reviewed: September 1, 2007