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Imaging System Measures Space Vehicle Surfaces
3-D measuring and digitizing systems allowed NASA to develop and test the Autonom Crew Return Vehicle X-38.
by Philip Colet
October 2003Top and rear views, respectively, of the Autonom Crew Return Vehicle X-38 demonstrate its "as-built" verses "as-designed" configurations. Color plot, which shows the deviations from the actual model versus the CAD data, indicates an excellent fit of the actual form to the CAD data.
During the 1990s, an important National Aeronautics and Space Administration (NASA, Washington, DC; www.nasa.gov) project concerned the development of the Autonom Crew Return Vehicle (CRV) X-38. This
vehicle was structured to transport as many as seven astronauts back to Earth safely in case of a mission emergency. During vehicle development, flight and landing tests were made at increasingly lower altitudes. Based on the results of these experiments, computer simulations of the vehicle were confirmed and refined to optimize the final design and to ensure maximum safety.
A crucial element in the success of this project was Computational Fluid Dynamics (CFD) software, which ensured that the form of the intended vehicle model matched the form of the object used in the simulation. For this reason, the surfaces of the models were optically measured and digitized using cameras, frame grabbers, image-processing hardware and software, and optical scanner sensing and 3-D digital photogrammetric systems that provided high accuracy and high data density during the vehicle development process.
Computer-Aided-Design (CAD) data were generated from the model data and used in the object simulation process. A digital surface-measuring process was needed because of the large size of the X-38 test vehicle; an 80% model measured approximately 33 feet long, 12 feet tall and 10 feet wide. Based on these data, multiple evaluation tasks were initiated, such as "as-built" versus "as-designed," generating an as-built surface model for CFD analysis and determining the effects of a previous "hard landing" test of the model.