For those who aren't familiar with Starfire, or who haven't played in a while, I thought I would post a little refresher on how Starfire colonization works.
The basis of production in Imperial Starfire is the Population Unit (PU). A PU is modified by the mineral wealth or lack thereof of its planet, and the race's tech level, and other modifiers, to find out how much mega-credits it produces a month. A planet, moon, or asteroid can have varying numbers of PU's, with asteroid having the lowest upper limit of 16, and benign planets having the highest limit of 3,200. It seems pretty straight forward, and it is. Except, this is Starfire, so everything has to be complicated. The complication comes with how many actual people the PU represents. A PU can represent anywhere from 50,000 to 22,500,000 people. This varies based on the number of PU's located on a planet/moon/asteroid. Mostly, you can ignore this, as it has no effect on the game, as PU's are the basis of production, not people. The only place this becomes important is in terms of colonization. All costs for colonization are calculated by Population Transport Unit, or PTU. One PTU equals 50,000 people. So, for smaller populations, one PTU = one PU. For a very large population, one PTU equals four hundred and fifty PTU's. This is how the economics of colonization work in Imperial Starfire. It doesn't make any sense to draw from a planet with a size of small, settlement, colony, or outpost, because it would deplete that population rapidly. Generally, planets with populations of the size medium, or 400+ PU's, are considered suitable for supporting colonization, as at that size one PU equals 18 PTU's, so drawing PTU's from a medium population for a full sized 150 PTU colonization mission would only reduce the medium population by just over 8 PU's. That's a winner for the colonizing race, as it is losing 8 PU's at the source population and gaining 150 PU's at the destination. You can boost a colony's population over 150 but doing so rapidly becomes very expensive. To boost a small population of 150 PU's to a medium of 400 PU's would take 650 PTU's to gain 250 PU's, whereas those 650 PTU's could be sent to five different habitable planets to gain 650 PU's of income.
Because of speed limitations, it is most effective to colonize systems within four jumps of your colonization-source. Anything farther than that increases the cost of colonization, and the duration that the cargo and quarters capacity is tied up. Colonizing more than four jumps out can be done, but in my standard Starfire campaigns it was rare.
That briefly is the economics of colonization in Imperial Starfire. In the Cold War campaign, I have drastically reduced the population growth rate to 20% of normal, if I remember correctly. This has affected the economics of colonization a lot, and in ways I didn't expect. Under the standard rules, generally by the time I had colonized the worlds within four jumps of my main colonization-supporting planets, some of the new colonies had grown to medium size and were thus able to support colonies themselves, extending the range at which colonies would be placed. This is not true in the Cold War campaign. Only after about 200 turns have colonies planted in the early days of the game grown enough to support colonization. This means that all of the major races were discovering planets in the 5-8 jumps area, or even the 9-12 jumps area, that they cannot cheaply colonize, because their only source of colonization remained their home planet. I soon realized that I was going to have to colonize planets in the 5-8 jump range band, and that I was going to have to force-grow colonies to medium size to support colonization efforts by shipping in PTU's to grow the population, rather than relying on growth. All of my races have been engaged in this practice, some more effectively than others.
Generally, there are three kinds of colonization taking place in the Cold War campaign.
The first is in-system colonization, where a medium size population ships PTU's to the other planets, moons and asteroids in the same system. This is cheap and effective, because each system will support a limited amount of free in-system colonization based on its productivity, and this can greatly increase the wealth generated by the system. For example, the Rehorish Home Planet produces 12,357 MCr's per month. The Rehorish Home System, which is fully colonized, produces 17,872 MCr's. The real drawback of this form of colonization is the time requirement it forces on the player in real life. Even with Starfire Assistant to help, it is probably the most time-consuming part of each turn, except for actual battles.
The second is standard colonization of newly discovered planets with 150 PU/PTU colonies. Both the Alliance and the Colonial Union have been forced by slow population growth to colonize in the 5-8 jump range-band, and sometimes even farther out than that.
The third is population-boosting colonization, which the races are using to boost the population of existing colonies to and past the 400 PU level so that it can support both in-system colonization, and the colonization of nearby habitable planets. This is very expensive and resource intensive, since it ties up large amounts of the race's freighters and colony transports. Generally, my races have reserved this type of colonization for benign/very-rich planets, or strategically or economically important systems.
The slow population growth in this campaign has really caused a problem for the humans in the campaign. Since Earth was largely bombed out early in the campaign, they lost their source of nearly limitless colonization, and this has affected all human successor states. Because this is the first time I've used the slower growth rates I did not anticipate how it would affect humanity. The Colonial Union ruthlessly plundered the remaining population on Earth to fund a massive colonization spree in the aftermath of the war, and this was effective, but has depleted Earth's population to the point where it is no longer the largest population in the Colonial Union.