^U.S. Department of Defense. Advanced Research Projects Agency. (1961, July 20). ADDENDUM to: Proceedings of Symposium: Project Vela (1st ed.) (263145). Washington, DC: U.S. Government Printing Office. Retrieved May 24, 2017 from the World Wide Web: [https://web.archive.org/web/20181030150429/http://www.dtic.mil/dtic/tr/fulltext/u2/263145.pdf Article title].