Barbara Bain had put up quite a squawk as soon as she saw Joan Collins's wardrobe for the episode, demanding that her skirt be longer, so as not to appear sexier than herself. Gerry Anderson refused the "request", explaining that Collins's legs were one of the reasons she was hired for the episode. As a result, Bain spent the last half of the show dressed in barbarian garb that was shorter than Collins's. Hence, the nickname "Barbara Pain" Anderson's crew had come up with early on during the show's production (not to her face, of course).
The Darian radiation suits were left over from the Catherine Schell film Moon Zero Two (1969), a movie Space:1999 SFX masters Brian Johnson and Nick Allder had also worked on (with one of the helmets originally being part of a spacesuit used on Gerry Anderson's film Journey to the Far Side of the Sun (1969).
Joan Collins (Kara) played Edith Keeler on the Star Trek (1966) episode The City on the Edge of Forever (1967). She and Karl Held (Jerry Travis on 1999's season two episode The Immunity Syndrome (1977) and Lindstrom on Star Trek's The Return of the Archons (1967)) are the only actors to appear in both Space:1999 and Star Trek.
Barry Morse had previously appeared on an episode of The Starlost (1973), a television series with a similar setting to this episode: a generational starship that had suffered a catastrophic accident several hundred years earlier.
This episode and The Infernal Machine (1976) are the only season one episodes that don't include Anton Phillips (Dr. Bob Mathias) in the cast.