There is no musical score for this film. Instead, each spacecraft has its own ambient soundtrack when it is shown in space. The Apollo shots feature a low hum; the XRV, a hollow ringing; the Nimbus Weather Satellite, a rapid series of beeps ascending in pitch; and the Russian Voshkhod, a constant pitch series of beeps. The only exceptions to this is are a very slight, muted bit of music played under the Apollo ambient soundtrack during Pruett's final EVA, and a single tone (with some ambient effects that could be called music) during the opening credits.
In the film, the astronauts are seen using what appears to be the early concept of the Manned Maneuvering Unit - during the real-life Skylab missions, the Astronaut Maneuvering Unit (the AMU) was tested inside the space station and never tested in the vacuum of space. The first use of the MMU was during STS-41-B (the fourth flight of the Challenger) on February 7, 1984.
Frank Capra began work on the film. Inspired by his work on the Martin-Marietta Corp.-commissioned faux documentary, "Rendezvous in Space" for the 1964 World's Fair in New York, Capra (a chemical engineer by education) worked to make the picture for Columbia, but finally abandoned the project in preproduction in May 1966 when he couldn't bring the budget down to the $3-million required by Columbia worldwide production chief M.J. Frankovich. The eventual budget for the finished film (directed by John Sturges) was $8 million. Capra never made another film.
The Film Ventures International re-edit of this film (retitled "Space Travelers") was featured on an episode of Mystery Science Theater 3000 (1988). This was also the only film featured on the show to have won an Academy Award.
Based on a novel by Martin Caidin, who would later write "Cyborg", the basis for the TV series The Six Million Dollar Man (1974).