interiors, always with the interiors some people.
One thing I recall from watching old episodes on tape that I
begged or bought for reference,
that the one shot of two live action actors seen
through the windows on the model is that they just couldn't fit in there.

Watch for that shot if you have an episode with it,
look closely and think about it,
you'll see what I mean.

This, me and my friends later called the 'Gerry Anderson Continuity Problem'.

To put it another way, the live sets occasionally bear little relation
to the models and vice-versa.
As to scale, looking at the pod door for example
and comparing it to the size of a human in the full size interiors
makes this model about 24th scale or within the vicinity of that.
So a couple of 24th figures were converted to Alpha astronauts and moulded off.