^Again, I think it's ameliorated by the fact that the people who smuggled him aboard were some of the people in charge of the ship's security in the first place. If he'd been some outsider trying to sneak aboard with no help from anyone on the expedition, it would've been completely absurd. But it was an inside job. He was probably smuggled aboard in a container brought by Hiroko or some of her allies, people who were authorized to be there and who had the access and authority to bypass whatever sensors or security systems needed to be bypassed.