here is an idea on how to journey to Alpha Centauri, using ion engines propell the ship to near the speed of light stop at Alpha Centauri then head back again. Now of course there are some problems with that. First ion engines take a long time to speed up, now if you had nuclear engines as well as ion engines you could zoom forward with a short burst gaining a lot of speed. Now another problem is how to get enough energy, solar panels is the best option but how would you get enough energy the answer of course is a laser. The laser would have to be extremely powerful in order to reach the ship, and it would need to be orbiting the sun in a perfect alinement in order to reach the ship and, the ship would have to have spare solar panels. the laser would be inside a space station pointing at the ship well orbiting the sun .