The Production Guide
Script To Screen: Earthbound
by Martin Willey

The first scene shot for the episode is an action scene, 66, as Simmonds shoots two guards (Steve Paterson and John Aston) to enter the nuclear power station. The signs by the door will be removed for the following scenes. According to the call sheet, wardrobe supplied pads for the actors who were stunned (probably knee and elbow pads worn under the costume, and possible floor pads as well, as the camera angle stops us seeing where they fall).

The second scene, 55, has Simmonds urging Koenig to seize their ship, as they walk down the corridor. There are a couple of female extras in background (one is Lesley Stamp).

The big scene of the day, while third to be shot, is earlier in story chronological order. Zantor and the Kaldorians arrive on Alpha, with other 30 Alphans watching.

Finally scene 80, from near the end of the episode. Simmonds has Zantor hostage; Koenig, Helena and Bergman shake hands to say goodbye.

The next "set" is the travel tube, but it is built at the end of the corridor set, and for at least two of the three scenes, they shot in the reception area of corridor, not inside the travel tube. First is scene 20 with Koenig and Helena, detailed here, but cut from the episode.
Next, scene 54 is between Simmonds and Koenig and leads directly into scene 55, filmed just before the crowd sequence. It is likely director Charles Crichton decided to move the dialogue to the start of corridor scene 55 to make one continuous sequence.
The third scene, 64, had Simmonds making his way into the travel tube with Koenig's commlock and a stun gun. We see this sequence in the episode.

In the afternoon, the crew moves to the regular stage L for the scene in Medical between Zantor and Helena. Although the day was an extended one, running past the normal finish at 5:30 PM, they didn't complete the scene today. It would be carried over to the following Monday.