When i hear about realistic interstellar travel, I think about solar sails. This addition could also utilize lasers as propulsion away from sunlight, and use sunlight to move it when in range of a star. And of course a near infinite energy source comes at the expense of a very large craft, and a slow retraction speed when you want to slow down or stop. The thrust would be controlled by how far the sails are extended, the smaller the area, the less thrust.