1. Aviation Image Library. (2018). Tupolev Tu-155. AirTeamImages. https://www.airteamimages.com/tpolev-tu-155_CCCP-85035_tupolev-design-bureau_354061.html
2. Barilo, N. (2015). Safety Considerations for Hydrogen and Fuel Cell Applications. Hydrogen Tools, Portal. https://h2tools.org/sites/default/files/Safety_Considerations_for_Hydrogen_and_Fuel_Cell_Applications.pdf
3. Bellis, M. (2019). History of Airships and Balloons. ThoughtCo, Life Long Learning. https://www.thoughtco.com/history-of-airships-and-balloons-1991241
4. Bogaisky, J. (2019). Startups bet hydrogen Fuel Cells are ready for takeoff in aviation. Forbes Magazine.https://www.forbes.com/sites/jeremybogaisky/2019/08/14/zeroavia-alakai-hydrogen-fuel-cell/#2cc402b918aa
5. BrewerG. D. (1919). Hydrogen aircraft technology. CRC Press.