Harris, Alexandra; Harris, Ray (2006). "The need for air space and outer space demarcation". Space Policy. 22 (1): 3–7. doi:10.1016/j.spacepol.2005.11.004.
Sanz Fernández de Córdoba, Dr. S. (24 June 2004). "The 100 km Boundary for Astronautics". Fédération aéronautique internationale. Retrieved 28 December 2020.