The Main Mission set ended up with much more foam than originally intended; the foam machines were so loud, the operators were unable to hear the director, Charles Crichton, ordering them to shut them down. According to Zienia Merton, Crichton finally ran out into the corridor where the foam machines were operating, waving his arms, yelling "Stop the bloody foam!", sliding on the floor, and disappearing into the enormous mound of soap suds. Nick Tate recounted that an unsuccessful search began for the hapless director, but three minutes later he emerged, resembling the abominable snowman, which everyone got a kick out of except for him.
The music highlighting the Brain's attack is "Mars, Bringer of War" by Gustav Holst, arranged by Malcolm Sargent. James Horner composed a variation of it for Aliens (1986) (for the scene of the Marines inside the alien hive).
Originally filmed December 5th to the 19th, 1974 (Zienia Merton turned 29 during filming). Additional footage was shot to replace scenes to be deleted (along with new scenes for The Last Enemy (1976)) from February 25th to the 28th, 1975, after all 24 episodes had been filmed, making "Space Brain" the last Season One episode to have filming completed. That final day of filming, which involved Main Mission being filled up with soap suds, took longer to complete than planned. Season One's "wrap party" was taking place at the same time, causing some of the actors to become disgruntled and anxious to join the party. During the wrap party, it was discovered that if the show were to continue into a second season, Sylvia Anderson would not be involved due to the Andersons' marriage about to come to an end.
First time showing that many among the crew are jigsaw puzzle enthusiasts.
The show's producers decided that they weren't satisfied with the episode's originally filmed ending, as well as the ending of The Last Enemy (1976), so new scenes were filmed for both immediately after The Testament of Arkadia (1975) was finished shooting (which had previously been intended to be Season One's finale). This episode originally ended with the Alphans all wearing spacesuits so all of the airlocks could be opened up, in which the lack of pressure differential would allow the moon to safely pass through the Brain without any harm to Alpha or the Brain. After putting the episode together, it was decided that a more dramatic conclusion was needed.