They are doing the work outside, this I can see and understand.
I see a door frame and a large door to the left. Why is there a door frame and no building?
Or is it a convertible building? The sides can go up in a few minutes?
And what’s with the headbands? Almost every man in the picture is wearing a headband; they appear to be color-coded.
This was before my time. I can’t answer your question, with knowledge. When I first saw the picture I thought it was a Soviet rocket because that is how they integrate their satellites with boosters.
Could it have been an inflatable building?
There looks to be quite a large blower apparatus in the background, with a large-diameter flexible hose. That might have been used to maintain positive pressure within.
As to why they took it away for this picture, I have no clue.
The door with no building certainly looks odd, doesn’t it?
Kind of reminds me of Les Nessman and his phantom office.
The building is on a rail that can slide in and out of place to protect against inclement weather. You can see the rail at the bottom left of the picture. They probably had the building open because it was a warm August day and too warm to work inside (probably little AC in August 1961). White Sands has a similar building that can slide back, and then the payload raises up vertical on the launch rail.
The amazing thing to me is none of the workers are wearing ground straps. Maybe because the booster is liquid-fueled they weren’t as worried about accidental ignition?