The James Bond movie series (which was also filmed at Pinewood Studios) was in the midst of a three-year hiatus (the disappointing sales of The Man with the Golden Gun (1974) leading to a shake-up of ownership of the franchise), so the set for M's office was used as the office of Commissioner Dixon.
At the start of the episode, Dr Russell says it was the 877th day since they left Earth orbit, so that makes the date February 3, 2002.
Much of Tony Cellini's role in the original script was meant for Alan Carter. Nick Tate described the story as very much resembling Alien (1979).
Nick Tate had been informed that he'd be starring in this episode, involving flash-back scenes of Carter investigating a space station whose crew had all been killed by an alien creature. However, Martin Landau objected to having another regular cast member upstaging him, so Landau had a heart-to-heart with Tate ("I'm the star, kid. When you have your own series, you can have control."), then personally assisted in a re-write (along with Gerry Anderson and Director Charles Crichton, adding the guest star). Tate was devastated that he was no longer the star of the episode but sympathized with Landau's point of view.
In this episode, we see the frame of the Eagle detach from the passenger module, and the command module separate from the Eagle frame.