 Footage of the US Jupiter spacecraft in the film is actually film of  the real Gemini spacecraft which flew between 1965 and 1966. The  Gemini spacecraft were used for testing of such activities as EVA  and docking for the Apollo space project which was to follow.  Ironically, the Soviet spacecraft in the film were called Gemini  (the name of the real life US spacecraft) and their designs were  based on inaccurate UK perceptions of what the Russian Voskhod and  Vostok spacecraft looked like, something which was not known until  1967 after the film had wrapped shooting.