The National Aerospace Initiative (NAI) was conceived as a joint effort between the Department of Defense (DOD) and the National Aeronautics and Space Administration (NASA) to sustain the aerospace leadership of the United States through the acceleration of selected aerospace technologies: hypersonic flight, access to space, and space technologies. The Air Force became concerned about the NAI's possible consequences on Air Force programs and budget if NAI program decisions differed from Air Force priorities. To examine this issue, it asked the NRC for an independent review of the NAI. This report presents the results of that assessment. It focuses on three questions asked by the Air Force: is NAI technically feasible in the time frame laid out; is it financially feasible over that period; and is it operationally relevant.