Why was the stowaway there?

When they were questioning him in the beginning he said he was arming something for the launch. He mentioned that he though he was clipped in. I guess he hit his head and passed out. I don't remember much explanation beyond that.

I still don't get how he would end up screwed in the thing like that though, without anyone seeing a huge man in a critical component... I didn't see much room for a crawlspace for another way for maintenance to get in the ceiling.

I kept expecting for them to reveal that he stowed away on purpose, and I still kinda feel that he might have. If that is the case maybe someone helped him get in there and screwed him in.

How come no one noticed a member of their team missing? Didn't he have any friends at work? Didn't he have a foreman he had to report to before launch? "Yeah, one of my technicians, who was working inside the spacecraft didn't come back and is missing but no big deal, I'm sure he'll show up."

Short answer, no, they did not even seem to think about how someone would be pushed up against the ceiling, or whatever it was before the launch, and screwed in behind a panel so tightly. It was really terrible this movie, and as bad as it was they seemed to keep doubling down on making it worse.

I liked the movie, but there was no explanation of how he got from the launch vehicle into the space station (or whatever it's called), and tucked up in a ceiling space behind a screwed-on panel, all by accident. It makes no sense.

I would think the extra weight would be noticed by sensors before liftoff. If no sensors, then liftoff might not be possible, but a problem would have occurred, been noticed, and researched,

I'm so glad you asked this question. I'm about half-way through the movie and undecided about whether or not to finish it. This was one of the things I really wanted to know and if that isn't answered, I'm not sure I want to keep going.