What good are colonies? By colonies here I mean those with large populations.
I built some colonies on the assumption that they are a good thing to have in any space 4X game. Now they are big enough (~50m pop each I think) and growing at a high enough rate (~10%?) that they are consuming a large and ever growing amount of my HW's production and D* stock just supplying them with infrastructure so they don't run short of housing and get annoyed. One has enough D* potential/production that if I hauled enough industry there it could probably build its own infrastructure, but its D* supply won't last forever and one of the reasons I built the colony there in the first place was a plan that it could mine D* and ship it to the HW. I can foresee this infrastructure problem growing as the colonies continue to grow.
I can see the value of colonies to man mines which are cheaper than automated mines to produce. Also, once the HW resources are mined out, the existing mines are useless there but can function on colonies that have resources to mine. Of course eventually those colonies resources will also be mined out and the process would have to be repeated at a new colony site. Assuming of course that you are lucky enough to find an inhabitable world that also has decent mineral resources. But then what do you do with the original colonies that keep demanding more and more infrastructure? Let them go in to revolt?
Traditionally colonies ship raw materials back to the homeland to feed industry there. As the colonies mature, they develop their own industry and eventually end up trading with the homeland (or rebelling of course and going their own way).
Aside of manning mines, the only real advantage I see to pop on colonies vs leaving the pop on the HW is the growth rate on colonies seems to be higher. Should I reverse my colony ships and start siphoning off pop to return to the HW to grow the tax base? I would of course be fighting against the efforts of the civilian colony ships. I can think of a bunch of small uses for colonies but I'm asking about the big picture here. I tried adding research centers to colonies so I could research more than one technology at a time, but I see little real benefit to that vs just researching one thing at a time on the HW faster.
Although there are a number of reasons to establish colonies, one possible strategy would be to stay at home and use automated mines only, shipping all of the minerals home. There are some disadvantages to a stay-at-home strategy, which are the opposites of the reasons for colonies, but it would make an interesting game. Before I list the reasons, it's worth pointing out that Aurora has realistic growth so building up colonies takes time. This is partially influenced by playing Starfire where the Rigellian Empire went from single planet of several billion to a galaxy-spanning colossus with a population of trillions in about 15 years :). I wanted the history of Empires to be more realistic in terms of what could be achieved over time. Something along the lines of the history of Weber's Terran Federation, which was measured in hundred of years.
Here are 10 reasons for populated colonies, as opposed to automated mining sites and listening posts (I am sure there will be others I haven't thought of while writing this list):
1) Homeworld minerals tend to run out in the first 10-20 years of a game. If you can find a planet with good mineral deposits, you can place twice as many manned mines as you could automated mines for the same production costs.
2) Some officers have great research bonuses but they are too junior to be governor of the home world. If you establish a small research colony, the required rank is much lower. Assign the officer and then build up the colony. Having several specialised research colonies will result in faster overall research than researching everything at home regardless of specialization.
3) Ships need maintenance and overhauls, as well as a base where that can sit without accumulating time on their maintenance clocks. All of these require maintenance facilities, which in turn require population to man them. Although you can explore and project power 3-4 systems from the home world, your survey ships will soon be spending more time in transit then exploring. Establishing forward bases will allow you to expand more easily, using the base as a node. It can overhaul survey ships and can serve as a forward base for warships. If you are at war with an alien race, establishing a colony with maintenance facilities close to their territory will allow you to forward deploy ships without running up their clocks and create a defence in depth.
4) Population growth is much higher on colony worlds. In some games (such as my current campaign), lack of population can be a major problem so increasing it can become the primary economic goal, in which case a lot of small colonies is a good way to achieve it.
5) Another bonus of greater population is greater wealth production, so if you are short on wealth, creating colonies can increase the growth of the Empire's overall wealth.
6) If you build spaceports on colonies, you can create trade routes that generate more wealth. Some planets have a rare trade goods bonus that will increase the wealth from trade routes. The Commonwealth in my current campaign is generating 25% of its income from trade.
7) You can specialise colonies to take advantage of officer bonuses. As it is difficult to get an officer that is good at everything, you could move your ordnance factories to a different colony and assign a officer with a 30% production bonus. Another colony could be setup for shipbuilding and assigned an officer with a 30% shipbuilding bonus. A third for mining, etc. New colonies can also be assigned governors of lower rank so you can take advantage of junior officers that wouldn't be able to manage the homeworld.
8) Ruins can be a good source of installations. Rather than bring them all home, use them as a basis of a new colony, bring in population and only remove what it is unnecessary.
9) As known space gets larger and sources of minerals close to the homeworld are exhausted, it can be worth moving those industries that require minerals closer to new mining sites.
10) A planet with a good amount of accessible sorium can be the fuel production centre of the Empire. Rather than bringing the Sorium back to the homeworld, put mines and fuel refineries (and an officer with good production/mining bonuses) on the planet.
I note in your answer you mentioned infrastructure. Worlds with colony cost zero don't need infrastructure so It's a good idea to build terraforming ships and select planets that can be rapidly terraformed. The best place to analyse this is on the Available Colony window (ctrl-A from the main menu or the World icon on the System Map).
Steve
