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The working title of this film was Threshold of Space. The picture closes with a voice-over narration explaining: "The experiments you have seen in this motion picture are reproductions of actual aviation medical experiments being performed by the USAF. The rocket sled and balloon gondola are real, not science fiction...There is no height, no depth the spirit of man, guided by a higher spirit, cannot obtain. These experiments continue..." The following written acknowledgment then appears onscreen: "The Twentieth Century-Fox Film Corporation thanks the United States Air Force for its generous cooperation in the production of this motion picture."
According to the Daily Variety review, some scenes were filmed at Eglin Air Force Base in Florida and Holloman Air Force Base in New Mexico. Although Hollywood Reporter news items add Nico Minardos, Rex Lease, Jesse Kirkpatrick and Leonard Penn to the cast, their appearance in the released film has not been confirmed. John Hodiak died of a heart attack on October 19, 1955, just after completing his key scenes in the film. The studio decided to eliminate several minor scenes featuring Hodiak that had not yet been filmed, according to a October 20, 1955 Hollywood Reporter news item. On the Threshold of Space was Hodiak's last released film.