(at around 52 mins) As Cdr. Walker's mental condition worsens, he mutters "Fate has ordained the men who went to the Moon to explore in peace remain on the Moon to rest in peace." This line paraphrases the beginning of a contingency speech, drafted by speech writer William Safire in a memo entitled "In Event of Moon Disaster," which was intended to be delivered by President Richard Nixon in the event that the Apollo 11 astronauts were stranded on the lunar surface without hope of rescue.
The prologue text at the beginning of the movie states that the documented footage of the secret Apollo 18 mission was uploaded to the website "www.lunartruth.com". If you type that address into your browser, it redirects you to "apollo18movie.net", which is the movie's official website.
(at around 18 mins) After the first resting period the astronauts are listening to 'Cheap Day Return' by British rock band Jethro Tull. Tull's third album 'Benefit' contains the track 'For Michael Collins, Jeffrey and Me', a song which refers to Apollo 11's command module pilot Michael Collins. In the song vocalist Ian Anderson sings about the feelings of the command module pilot, being left alone above while others get to walk on the moon, something which is also referred to during the movie.
In some way, there was a real Apollo 18 during the year 1975. Named ASTP (Apollo-Soyuz Test Project), the mission was the first docking of spacecrafts built by different nations. The American crew included one of the seven Mercury program astronauts, Deke Slayton (the one who had never flown) and the Russian one Alexey Leonov, who was the first man to "walk in space."
NASA's liaison for multimedia, Bert Ulrich, has officially stated that "Apollo 18 is not a documentary ... the film is a work of fiction."
The actual Apollo 18 lunar mission flight crew would have been the Apollo 15 backup crew: Richard Gordon (Commander), Vance DeVoe Brand (Command Module Pilot), and Harrison Schmitt (Lunar Module Pilot). Because of his expertise in geology, Schmitt was moved to Apollo 17 after Apollo 18, 19, and 20 were canceled.
(at around 1h 16 mins) The closing audio clip consists of excerpts from President Richard Nixon's speech in Honolulu on April 18, 1970, as he presented the Presidential Medal of Freedom to the crew of Apollo 13; his reading of the medal citation was edited to remove him saying "13" both times that he refers to Apollo.
The character of Lt. Col. John Grey was less prominently featured in earlier versions of the film.
The opening scenes introducing the three main characters was the last footage shot for the movie.
The release date was moved several times, from March 4, 2011 to April 22, 2011, then an almost entire year to January 6, 2012, then it was advanced to August 26, 2011 and finally was released on September 2, 2012.