Out of all of the episodes made for the series, four episodes no longer exist on their original broadcast-quality formats - two from the first season are lost as are two from the second season - and are thought to survive only as domestic off-air recordings. The following seasons survive intact.
Earth "explorers" would wear sweaters identifying them as members of the Galactic Archaeological Society.
The series pilot was never broadcast. Featuring a live audience, it overran in studio - and also contained a game involving the electrical conductivity of salt water, something it was felt was highly inappropriate for a series which children would be watching.
Bill Homewood was hired as backwards-speaking Australian Ron Gad after Ian Oliver recalled witnessing him sing "Puff the Magic Dragon" in reverse on the first edition of Multi-Coloured Swap Shop (1976).
Paul Darrow did the fifth show of Series 1 between seasons of Blake's 7 (1978) which he starred as Kerr Avon.