Thunderbirds is so easy :)
"You can't see the unopened one beforehand - unless of course, it's a (disguised) sea blue colour. :)"
The sides of the cardboard box facing the camera are 'Green' ...... so they can use 'Green Screen' techniques to overlay a video feed of the ground *without* the cardboard box over the cardboard box. !!!??? (You know what I mean :) )
They then flip the cardboard box around and stand it up, image of landed rocket on 'Green Background'.
'Green Screen' it again and done !!!
(No strings or marionettes needed) :)