All three sets have the small zigzag slots shown at top. I suspect these have served for looping a rubber band round 3 - 4 astronaut figures (depending on the set) similar to how it's done on the GA Moon Exploration boxed set (qv).
The Nuclear Freighter is somewhat precariously held by loops around its exhausts and nose.
Box size
Length
Width
Height
49 cm
34 cm
7 cm
19 1/4 in
13 1/2 in
2 7/8 in