Canadian astronaut Chris Hadfield is interviewed by Linda Wertheimer on NPR’s Morning Edition and explains one of the reasons we have an International Space Station:

For thousands of years, people sailed in rivers and up and down the coast. And only after they had invented so many things - navigation, food supply, really good sails, ships they could count on - did they turn away from shore and go over the horizon. They had to invent a lot of things first. There may have been people that went over the horizon, but they probably didn’t come back, because they didn’t know enough stuff yet.

And we are, right now, sailing within the sight of shore. We’re trying to figure out all those things as we go around the world, so that when you do fire your engines and go 40 percent faster and leave the Earth, and it’s been really hard to turn around and come back, that you can count on your sailing ship, that it’s going to keep you alive and get you where you want to go. And that’s what the Space Station is. It is the crucible where we’re learning and testing and figuring out all those things so that we can go further, which is inevitably what we’re going to do.