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flightglobal.com
"The First Day In Orbit". Flight. 80 (2736). London: Iliffe Transport Publications: 208. 17 August 1961. Archived from the original(PDF) on 2019-06-03. Retrieved 2009-03-12.
"Missiles and Spaceflight"(PDF). Flight. 80 (2741). London: Iliffe Transport Publications: 467. 21 September 1961. Archived from the original on 2019-06-03. Retrieved 2009-03-12.
"The First Day In Orbit". Flight. 80 (2736). London: Iliffe Transport Publications: 208. 17 August 1961. Archived from the original(PDF) on 2019-06-03. Retrieved 2009-03-12.
"Missiles and Spaceflight"(PDF). Flight. 80 (2741). London: Iliffe Transport Publications: 467. 21 September 1961. Archived from the original on 2019-06-03. Retrieved 2009-03-12.