2. The three limits: fields, energy and crew

Production on a world is throttled by three separate things, and they are deliberately different in kind. Two of them you can research your way around. The third you cannot.

Building fields

Every world has a finite number of building fields, and every structure level occupies one. A world is therefore a set of choices rather than a checklist: a world covered in mines has no room for a shipyard, and one covered in defences has no economy behind it. A Command Nexus adds two fields per level; beyond that the only way to get more ground is the Terraforming Array.

The energy grid

Every structure draws energy; reactors and solar arrays supply it. Take more than you make and the whole world's production falls proportionally – a brownout, not a shutdown. Superconductor Grids cut what every structure in your empire draws – it is worked out as a divisor rather than a discount, so ten levels is about a third less and never anything like free. Reactor Physics raises every reactor and solar array by 6% per level. And any mine can be throttled to 75%, 50%, 25% or 0%, which cuts its draw by exactly the same proportion as its output – that is the lever to pull while a reactor upgrade is still building.

Crew

Structures need people. Crew grow in Habitat Domes up to that world's housing, and a world short of crew produces less in the same way a world short of energy does – though in practice a world built to a sensible shape runs out of ground and power long before it runs out of people. What crew really decides is how freely you can move your empire around: crew cannot walk, and the only way to shift them is aboard a hull with pressurised berths – a Star Freighter, a Fleet Carrier or a Colony Ark.