Hey,
I tried to set a harvester to automatically harvest from gas giants and drop fuel off at colonies when it was done (Conditional order A: Fuel tanks full, unload fuel at colony and move to sorium gas giant). Jupiter and Uranus have massive amounts of of Sorium in them. My harvester can harvest well enough, but when it comes time to drop off the load, it only drops it off but doesn't fly back to a gas giant. Instead, it just tells me that its orders are complete.
Any help would be much appreciated.
The usual technique is to have tanker ships which pick up fuel at the harvester and drop it off at a colony. The reason for this is the usual specialization thing: while the harvester modules are working, the engines (on the harvester) aren't, and vice-versa. So if you try to make the harvester fast enough to drop off fuel and get back in a reasonable time, then you're going to pay a lot of cost and mass in engines that just sit there idling most of the time. Putting the engines on a separate tanker allows you to use them for other tanker-type things when you're not shuttling fuel.
You can take this to an extreme - build the harvesters without any engines, and build a few tugs that can tow them where they need to go as they come off the production line. Similar statements apply for terrraformers, asteroid miners, etc.
John