Starbases were the foundation of the old republics defenses during the pirate wars. They could control entire planets, or even multiple. They can carry more weapons and armor than regular ships, but cant move. While the military overthrow the republic during the start of the big alien invasion, starbases were the only things holding the aliens back from breaking the front and conquering the core systems of the HDC. The new formed Human Defense Coalition didn't use starbases anymore, since they often couldn't hold positions for long enough to finish construction, so over the years of war, the old technology went to be nearly forgotten. One day, a crew of a smuggler ship discovered an old republic starbase, but the crew died ages ago of an unknown plague. They got captured after this, and described the location. After knowing of the cause of death, the smugglers and everyone in contact with them got executed, to prevent a spread. The HDC send a discovery mission, and tracked back how to build these. With modern technology, the HDC command ordered for a new generation of starbases and builders for them. They could be build with nearly anything available, and much quicker.
The process of construction: Starbases are very big, sometimes multiple kilometers long. To get this large amount of recourses, its important to build near asteroids, or your logistical costs would kill your empire before the enemy it does. A Starbase mission needs at least 2 ships: A factory ship and a constructor.
The constructor: It lands on a bigger object like an asteroid to get stability. Once it landed, it uses small drills to hold itself onto it. After this, it extends long arms, spanning a magnetic field. In this field, it melts metals together using a strong radiation module, and keeps the liquid metals in form until a small part of the construction is finished. The first melting takes the most energy, after this, the metal already gets warmed by the already molten one. After each section is constructed one by one, they get cooled down using laser cooling (its a real thing, google it). They than get put together carefully by cold welding.
The factory: The factory houses all equipment to produce every material the HDC knows in mass, given the right input. It can even synthesize some materials, but it takes much time and needs to turn all production lines off, to meet the energy requirements. The factory is slow, and only focused on production for the constructor. Some models have fewer fabrics, but factories for fighters and armor. they can restock carriers after a battle, but wont take part in any fight. To make live supporting systems unneeded in the actual production lines, they are automated by the most part, and under direct control of the constructor. The hearth of the vessel is its medium hangar, where dozens of big and small mining ships start to gather raw materials from asteroids and bring them to the factory for further use.
Since the radiation module had caused cancer in more than a few cases, HDC command decided to isolate the control room and let robots do most of the work. The combination and work progress is mainly controlled by a weak AI and other automatic systems.
