'The Triads' by Alan Fennell

After detecting a series of huge explosions in space, Commander Zero sends Steve, Venus, and Matt in Fireball XL5 to investigate the planet Triad, a recently-discovered world at the edge of known space. However, when the crew reach the planet its high-gravity causes the ship to crash land – then they meet Graff and Snaff, a couple of seemingly friendly giants…

Paul Maxwell (Colonel Steve Zodiac), Sylvia Anderson (Doctor Venus), David Graham (Professor Matt Matic / Lieutenant 90 / Zoony the Lazoon / Graff), John Bluthal (Commander Zero / Snaff), Gerry Anderson (Robert the Robot)

Directed by Alan Patillo
Produced by Gerry Anderson
Associate Producer Reg Hill

TX (UK - ITV):
24th June 1963

Notes:
*Featuring Colonel Steve Zodiac, Venus, Professor Matt Matic, Commander Zero, Lieutenant 90 and Robert the Robot