1. H. Taguchi, A. Murakami, T. Sato, T. Tsuchiya, Conceptual study on hypersonic airplanes using pre-cooled turbojet, AIAA 2008–2503, in: Proceedings of the 15th AIAA International Space Planes and Hypersonic Systems and Technologies Conference, 28 April–1 May, 2008, Dayton, Ohio.
2. E. Sänger, J. Bredt, A rocket drive for long range bombers (Über einen Raketenantrieb für Fernbomber), Deutsche Luftfahrtforschung, Ainring (Translated by Hamermesh, H. Radio Research Laboratory), August 1944.
3. Silbervogel Wind Tunnel Model, Source: 〈http://en.wikipedia.org/wiki/File:Silbervogel.jpg〉.
4. D.R. Jerkins, X-15 Extending the frontiers of flight. National Aeronautics and Space Administration, e-book available: 〈http://www.nasa.gov/connect/ebooks/aero_x15_detail.html〉.
5. National Aeronautics and Space Administration, X-37 Demonstrator to test future launch technologies in orbit and reentry environments, Fact Sheet nr. FS-2003-05-65-MSFC, Release date: May 2005, Source: 〈http://www.nasa.gov/centers/marshall/news/background/facts/x37facts2.html〉.