This I did as a front cover of a book a friend of mine is writing.
The ship is, basically, a 12 km long mothership that drops off a massive terraforming/power-station ship at each planet it visits. The mothership travels a figure of eight course, through the galaxy, dropping off fourteen of these dropships. So, by the time the mothership gets back to the first planet it visited, the dropship would have completed the terraforming process and started generating enough power to run the planet.
Or at least thats the theory.