Care should be taken when building these structures, as they can anger the colonists and natives (except defenses), especially when you are dealing with non-Avian Anarchists.
Mineral mines are the structures necessary to mine the minerals out of the ground. Again, care should be taken, as the planet will eventually run out of resources that may be mined. They cost four (4) megacredits and one supply each.
Up to twenty (20) mines may be safely built on any planet to avoid sensor sweep detection.
Factories produce the supplies that are necessary to produce additional structures, build fighters in space, perform alchemy, or sell for megacredits. They cost three (3) megacredits and one supply each.
Up to fifteen (15) factories may be safely built on any planet to avoid sensor sweep detection.
The percentage odds that an enemy planet will show up on a Sensor Sweep scan are: 100% - Defense Outposts * 6.66% (Unverified for Planets NU)
Sixteen (16) defense posts are needed to block sensor sweep regardless of the other structures (although fewer posts will prorate the detection percentage), and twenty-one (21) are needed to block a bio scan.
Protection against Super Spy
The ion pulse will decloak all ships in orbit upon trigger, but only has a 20% chance of actually triggering. If the friendly code has been changed to mfX, then the ion pulse will always go off as long the required defense posts are present.
Planetary defense posts contribute to a multiplier which is then multiplied by the racial ground defense to provide the final defense ratio. It is this final defense ratio that is compared to the attack ratio of the attacking race (usually the Lizards).
The multiplier starts at 1. Each defense post adds .05 to this multiplier. 20 defense posts will double your racial defense, 40 will triple it, and so on.