1. V.J. Bilardo, J.L. Hunt, N.T. Lovell, G. Maggio, A.W. Wilhite, L.E. McKinney, The benefits of hypersonic airbreathing launch systems for access to space, AIAA 2003–5265, July 2003, Huntsville, Al.
2. NASP Phase 2D Final Scientific and Technical Report A011 (DI-MISC-08711/T) F33657-91-L-2012, December 13, 1994.
3. J.L. Hunt, R.H. Ricketts, C.R. McClinton, Reference technology sets and readiness levels for hypersonic airbreathing vehicles, 200 JANNAF CS, APS, PSHS and MSS Joint Meeting, Monterey, CA, November 13–17, 2000.
4. R.L. Brown, Assessing technology readiness using a value stream process, Presented at NET Workshop on Processes for Assessing Technology Maturation and Determining Requirements for Successful Infusion into Programs, Marshall Space Flight Center, September 16–18, 2003.
5. Committee on national aerospace initiative, air force science and technology board, division on engineering and physical sciences: evaluation of the national aerospace initiative, National Research Council of the National Academies, The National Academies Press, Washington, D.C., April 2004.