"Rosetta mission: Philae craft may have bounced during comet landing - as it happened" by Stuart Clark, James Kingsland, www.theguardian.com. November 12, 2014.
"John F. Kennedy: 1961 : containing the public messages, speeches, and statements of the president, January 20 to December 31, 1961" by John F. Kennedy, Washington: Office of the Federal Register, National Archives and Records Service, General Services Administration, 1962.