We can easily make a long trip. All we have to do is use the idea from the movies and creat a central engine core and a rotating habitat. The centripital force would create a kind of pseudo-gravity. It would work. It's like tossing a ball up and down on an airplane. The ball is inside the plane's "sphere of inertia" as I like to call it, so the ball goes straight up, then straight back down again, relatively speaking.