Retrieved 25 March 2016. ↑ Space History Division 1999 ↑ "John Dennett: Isle of Wight Rocket Man". virgin.net. Retrieved 7 April 2015. ↑ "William Leitch Presbyterian Scientist". apogeebooks.com. Retrieved 22 November 2016. ↑ Tsiolkovsky's Исследование мировых пространств реактивными приборами - The Exploration of Cosmic Space by Means of Reaction Devices (Russian paper) ↑ Johnson 1995, pp. 499–521 ↑ Esnault-Pelterie 1913 ↑ "US patent 1,102,653".