In the movie he states "no one knows what's inside that cloud". So if there has been no trip to Titan, where are the other space trips going throughout that trip? They often shows spaceships leaving the earth and going SOMEWHERE. Vincent is always looking up when they take off.
I was assuming they all were going to Titan but now that I've re-watched this movie, well I'm not sure
I guess the other rockets are bound for nearer, but also habitable, destinations. You've got to assume that if we have the capability for a mission to Titan, we've already established outposts on the Moon and Mars, and possibly moons of Jupiter as well.
Can't remember if any of these are mentioned (or even alluded to) in the movie. But Titan is portrayed as the outermost destination for mankind at this time, and a place far enough away from the rest of humanity that the protagonist feels he might find solace there.