Oberg, James (1999). "The Nature of Space Power"(PDF). Space Power Theory. National Space Studies Center / US Air Force Academy. p. 53. Archived from the original(PDF) on 2018-07-12. Retrieved 2013-01-18.
Oberg, James (1999). "The Nature of Space Power"(PDF). Space Power Theory. National Space Studies Center / US Air Force Academy. p. 53. Archived from the original(PDF) on 2018-07-12. Retrieved 2013-01-18.