One major part of a starbase's function is to protect the planet it's orbiting, adding its five fighter bays, fighters, technology, and defense posts to the planetary defense. A well-defended starbase can stand toe-to-toe with any but the most powerful starships in the Echo Cluster.
The Defense command switches to the Fighter and Defense construction screen. Instant construction of fighters costs 3 Tritanium, 2 Molybdenum, and 100 MegaCredits per fighter. You may have up to 60 fighters in a starbase and you may put fighters on board any ship equipped with fighter bays. The fighters on board a starbase will be used to defend the base and planet against attack.
Starbase defense posts can also be built on this screen. Each costs 10 MegaCredits and 1 Duranium, and each adds damage resistance to the starbase equivalent to 1 KT of hull mass. Unlike planetary defense posts, starbase defense posts add no "free" fighters and do not increase default defensive weapon technology, but they can increase the number of beam weapon posts that will defend the planet in event of battle.
If a planet comes under attack the fighters on the starbase and the fighters on the planet's surface are launched against the attacking ship. Beam Weapons on the planet's surface and the beam weapons on the starbase will be fired against the attacking ship. The higher the combined defense strength of both the planet and the starbase, the greater the number and power of the planetary beam weapons. The tech level of the planetary defense beam weapons can also be improved by upgrading the beam weapon tech level of the starbase.
If a starbase is damaged in combat, that damage will accumulate through subsequent combats. (Although it will have no impact on base combat performance, damage will reduce starbase shipbuilding tech levels, which can be repurchased later according to the normal rules.) Damage can be repaired at a rate of 5% per turn with the Repair order, but if the total ever accumulates to a number exceeding 100%, the base will explode after that combat round.