Well, I was wondering, as the title of the thread says, What kind of atmosphere is in the cargo bay of the space shuttle during launch? There’s no reason to put breathable air in there, and the gases would just add extra weight. Is it pumped to a vacuum, or something?
Well, thanks for everyone’s time,
Yes, the cargo hold is vented to the outside. There’s no reason not to put breathable air. Using any other gas is dangerous for ground crews working in/around the cargo hold.
Pumping it out would require the doors and other structure to be stronger, therefore heavier, to take the pressure differential. That would certainly add more weight than removing the atmosphere.