Hmm......well you're serious so I will be too.
I've thought this same thing many times. My conclusion is not how DO we know, but how CAN we know?
The scientists say it's expanding. How do they know? They can't see the end. If you can't see the edge of the universe then how can you know it's getting farther away?
Think about this: Astronomers knew little about the universe. Over time they discovered our solar system is in a galaxy. They discovered our galaxy is a little one with an unknown number of other galaxies and solar systems. They keep finding more and more galaxies out there. The only definitive thing they've discovered is that they haven't discovered it all yet.
Another thing is, how can we even put into perspective how big the universe is anyways? I mean honestly know, not just saying, "Well it sure is big!" Well yeah it's big! So big we can't imagine the bigness of it.
The scriptures don't say anything about it expanding, and they don't say anything about it not expanding. They also don't tell us how much "space" [no pun intended] that the universe takes up.
Take a box. Take some balls and marbles and some cosmic looking dust and build yourself a little universe in there. Keep building, keep building, stop. The box isn't getting any bigger is it? You can't go any further. Is the universe God created in a box? If it is in a box, then what's on the outside of the box? If not, then what's on the other side of the edge of the universe? Is there empty space [again, no pun] out there waiting for more stars, planets and what not to be made, a rural empty space waiting for more urban and suburban space to be built? Is there a different universe on the other side?
Don't try to wrap your mind around it because you'll never get it. Questions will beget questions.
They do for me anyways.
Matt
p.s. Has it ever occurred to you just how long it takes to space travel in that ship you refer to? Let's say it's a self-contained ship that creates and recycles it's own fuel indefinitely. You're gonna have to take Leon's fountain of youth with you so you don't die trying to find the edge of the universe.