Ship system reliability and maintenance.
Every ship module has a reliability value. It depends on the quality of the module's design and construction, which in turn depend on the level of production, material quality, and workforce skills. Damage sustained and repaired, timely maintenance, age, and operation within permitted limits for acceleration, temperature, and so on also affect it.
Reliability itself affects how long a module runs before failure and how severe the damage is when it fails.
The player doesn't know the exact reliability value, but an inspection updates and displays one of four statuses: very reliable, reliable, unreliable, or extremely unreliable.
Ships therefore need periodic inspections and timely maintenance. To simplify things somewhat, maintenance intervals are grouped into multiples: 3, 6, 9, 12, 18, 24, and 36 months. Most modules can be serviced during flight, provided the ship has the necessary spare-parts kit and a staffed engineering section. Otherwise the whole ship must go into a dock or workshop. All these procedures can be set up as a fully automatic process: instead of taking its next assignment, the ship gives priority to traveling to a specified port, replenishing supplies there, and undergoing maintenance. Players can also handle everything themselves if they wish. Indicators in the flight planner will help them understand the situation and set priorities, including the option of skipping scheduled maintenance altogether.
The hull and structure have their own reliability value too. If their status becomes extremely unreliable, the ship risks catastrophic structural failure, making any repair impossible.