As brought up previously, sorium harvesters are best left stationary (or on a supertanker, if your fleet needs super-long-range support). Have another ship being ordered to "refuel from fleet" at the harvester and "drop 90% of fuel at X colony" so that your courier ship will run to the harvester, take fuel, run to the planet, empty fuel, and then click the cycle option so it'll keep doing it.