United States. Government Accountability Office. NASA: Issues Surrounding the Transition from the Space Shuttle to the Next Generation of Human Space Flight Systems, text, March 28, 2007; (https://digital.library.unt.edu/ark:/67531/metadc295311/m1/1/: accessed April 24, 2024), University of North Texas Libraries, UNT Digital Library, digital.library.unt.edu; .

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