[quote=@Host]
<Snipped quote by Blabbo>

Yes, the surprise.

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What do you have to think about when building for space travel instead of something like sea travel?
[/quote]

Two entirely different things. A sea vessel needs to be concerned about bouyancy, being sealed on its lower portion, etcetera. A space vessel needs to be able to escape the gravitational pull of any planet or moon it lands on, deal with cosmic radiation, circulate its own oxygen, maintain other resources needed for life, along with loads of other things you'd expect when dealing with a mostly empty cosmos.