We are exploring the ocean, but due to materials and knowledge, we have far less capability that we do exploring space. See, in space, there's so much mathmatics and small concerns that we have graciously expanded our knowledge in space travel. That and every single space disaster has changed how we approach the resolution of space colonization.
In fact, just to let everyone know, if we do use a pure FTL drive(IE something that comes CLOSE to the speed of light, relatively) time actually changes for those in the ship compared tot he galaxy at large.(ie 1 year on ship could be 100 years elsewhere). But we don't have the information, yet on how to manipulate or do said stuff.
In the same vein, though, we have found new methods of fuel using either existing sources(shale rock>gasoline) or new fuel sources(any kind of non fossil fuel gas/solar/wind/geo etc are all NEW energy sources). Sadly most of these are not "cost effective" so we rarely see them beyond demos, tests, or as curiosities. Once someone invents a way to get cheap fuel out of these sources, everything will change. In space, they've postulated using Hydrogen as a possible fuel source(being the most abundant gas currently known in our galaxy). I mean, Gas Giant? Yup lots of Hydrogen.
The thing that holds humans back isn't their capability to understand, it's our natural tendency to "be better than others," that does. Wars, Famines, Disease, Poverty, etc. will most likely follow us right up to the stars as well. We can't escape ourselves, no matter how hard we try.
