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In Sid Meier's Alpha Centauri (SMAC), the Planetary Transit System is a Secret Project. It may be built at a cost of 270 minerals, on discovery of Industrial Automation (B3). The Planetary Transit System starts subsequently founded bases at size 3; furthermore, all your bases less than size 4 have one less Drone.

How useful is this? Normally, the territorial expansion cycle goes something like this: Wait for a base to grow beyond size 1. Produce a Colony Pod unit, reducing the size of the producing base by 1 (simulating population transfer). Move the 'Pod to a good spot and found the new base. Wait for the base to grow beyond size 1 so you can produce more Colony Pods...
Owning the Planetary Transit System means a newly-founded base can immediately produce a Colony Pod (or even two!), drastically speeding territorial expansion. At the very least, the Planetary Transit System triples the value of your Colony Pod units.

This makes a particularly nice offset for the -2 Growth penalty associated with the Green economics model in the Social Engineering screen. It's brutal in the hands of the Hive faction (blue, Yang), as their faction design includes a free Perimeter Defense at every base, and +2 Growth.

In situations where you trust your neighbors not to invade an undefended base, the Planetary Transit System also makes roving Mind Worms less of a hazard to a newly founded base. An undefended size 1 base will be obliterated if invaded, but an undefended size 3 base attacked by a "wild" native unit only loses a size point. Annoying, but at least you didn't waste a Colony Pod.

The downside is that new bases are more sensitive to low food production in the production radius. If you don't have a farm or forest available to the new base, it may starve down a size point at the end of its first turn.

Secret Project animation narrative:
"As distances vanish and the people can flow freely from place to place, society will cross a psychological specific heat boundary and enter a new state. No longer a solid or liquid, we have become as a vapor and will expand to fill all available space. And, like a gas, we shall not be easily contained."
   -- Sister Miriam Godwinson,
   "But for the Grace of God"