The second episode broadcast, but the fifth episode filmed (between 13 May to 23 May, 1969).
When on Moonbase, female staff have purple hair while male staff have normal hair colors. When Lieutenant Ellis is on Earth her hair is its normal color. None of this is explained.
Matt Zimmerman (Foster's co-pilot) was dubbed by Jeremy Wilkin (Skydiver Navigator Lt. Gordon Maxwell). Zimmerman is best known as the voice of 'Alan Tracy' in the series Thunderbirds (1965) and sequel films Thunderbirds Are GO (1966) and Thunderbird 6 (1968).
Basil Moss (Dr. Frazer) is one of 11 actors to have appeared in Journey to the Far Side of the Sun (1969), the movie that led to this series.