1. http://www.nationalmuseum.af.mil/Visit/Museum-Exhibits/Fact-Sheets/Display/Article/198095/kettering-aerial-torpedo-bug/ [retrieved 24 April 2018]
2. Office of the US Air Force Chief Scientist "Technology horizons: a vision for Air Force science and technology 2010-2030" pp.123
3. "NASA Aeronautics Strategic Implementation Plan" 2017pp.5
4. https://www.nasa.gov/aero/nasa-embraces-urban-air-mobility 2017 [retrieved 24 April 2018]