Aerodynamic Testing in Support of Orion Spacecraft Development

*The Orion Spacecraft will operate in the Earth’s atmosphere during ascent, re-entry and during launch aborts. The Orion Project is therefore required to develop a comprehensive aerodynamics database for all flight regimes and vehicle configurations. Development of the flight control system for the vehicle depends on accurate aerodynamic performance and stability data. For the most part, the Orion Aerosciences Project is generating the necessary database using CFD. A coordinated experimental effort is underway to validate the various CFD codes used to develop the database and to provide aerodynamic data in flight regimes where the CFD is either less accurate than required or cannot provide timely answers (e.g. dynamic stability). Whenever possible, we will determine the aerodynamic coefficients from multiple sources, providing the best chance of understanding the vehicle behavior and the level of uncertainty in the database. HE new Orion spacecraft will provide routine access to low earth orbit for servicing the International Space Station (ISS) and the capability to return to the Moon. In order to successfully carry out its various missions, its flight through the Earth’s atmosphere must be accurately understood and controlled. The engineers who designed the Apollo spacecraft relied exclusively on wind tunnel testing to generate the aerodynamic databases for the various flight configurations for that vehicle. During the intervening 40 years CFD methods have become much more accurate and faster. As a result, the bulk of the aerodynamic databases for Orion will be developed computationally. Wind tunnel and ballistic range testing will play a key role in validating the computations over a wide range of flight conditions. The areas for which CFD is either less accurate than desired (M < ~1.1) or is not yet sufficiently developed (unsteady aerodynamics) experimental data will provide the necessary database information. Development of the aerodynamic configurations for Apollo and generating the aerodynamic databases required approximately 5,763 hours of wind tunnel testing from 1962 to 1964. The work included 110 wind tunnel tests in 19 different wind tunnels. 1 The tests were used not only to generate the aerodynamic databases but also to assist in design decisions, particularly in the development of the Launch Abort System (LAS). With this emphasis on the design process, the aerodynamic tests during the first year of the Apollo program tended to be short duration with numerous model configurations. The later tests were done on configurations closer to the flight vehicle and provided a more complete understanding of the stability and performance. In contrast, the Orion aerodynamic testing plan includes only about 40 aerodynamic tests in 7 or 8 wind tunnels and 4 or 5 ballistic ranges. The focus of the early tests was to validate the CFD methods to be used in generating the bulk of the aerodynamic database and to investigate techniques to experimentally determine the dynamic stability derivatives for the spacecraft. With this particular emphasis, the individual tests tend to be longer and involve multiple data types (force, mean and unsteady pressure, flow visualization, etc.). The result is that even with fewer tests than for Apollo development, we will complete nearly as many hours of testing. The development of the Ares launch vehicle to carry the Orion spacecraft to orbit also requires understanding of the aerodynamics of the full launch vehicle during ascent. Since the Orion is part of the launch vehicle, the responsibilities of the two programs have been carefully defined. During a nominal launch, the Orion is integral to the Ares launch vehicle while operating in the atmosphere and any associated aerodynamics of the launch vehicle is the responsibility of that Project. Upon the initiation of an abort below about Mach 6, the Launch Abort Vehicle (LAV) is considered a separate vehicle, the aerodynamics of which is the responsibility of the Orion Project.