No the assumption is that the magnitude of energy involved in interstellar travel is so large that it dwarfs all other considerations. If you can't afford to expend the energy to travel around the solar system to acquire resources, you definitely can't afford to engage in interstellar travel.

And then of course, if you can't afford the energy to sustain a human population on Earth in decent conditions, you also definitely can't afford interstellar travel. Because implicit in your assumption is that somehow the extremely limited number of people who could be put on a slow ship (and by slow we're talking thousands of actual years minimum at "current technology" levels) will somehow be able to command and control all of Earth's fissile resources.