Professor Hermann Oberth (1894-1989), German rocket pioneer, in Redstone Arsenal, USA,1956. Oberth envisioned the idea of a recoil rocket" which propelled itself by expelling exhaust gases. He developed this idea, considering how velocity was dependant upon the ratio of rocket mass to propellant and eventually concluded that space flight could be best achieved through multi-stage rockets. His doctoral thesis of 1922 on rocketry was rejected, but his work later became recognised as pioneering. Werner von Braun studied under him, and both were later instrumental in the development of the Nazi's V2 rocket, before continuing their work in the United States after the war."