This is the second time, the first being the first season War of the Robots, that Robby the Robot appears in. He is the robotic warden on the spaceship full of frozen convicts. The Prison spaceship itself appears in another first season show: The Derelict.
Debut of the cast's colorful/psychedelic costumes that reflected the cultural tone of the late 1960's. Also, from this point on, Lost in Space became a space travel show with planets-of-the-week, whereas they had spent each of the previous seasons stranded in the same two planets each time the ship was becalmed. Presumably this change was made to compete with Star Trek (1966).
Marcel Hillaire is the only actor in American television history to have appeared as a "plain" guest star (vs. the "special" designation accorded Jonathan Harris) in a show's both season opener & series finale - as different characters.
Angel Cartwright is noticeably taller and had matured considerably since the end of season 2. Her hair was the longest it had ever been and Irwin Allen didn't like how she looked like a hippie girl. The hair department came up with a way to fold her up and pin it so it looked much shorter.
This episode marks the debut of a new musical theme which, like the original theme for Seasons 1 and 2, was composed by John Williams.