Merit's Galactic Reunion - more mines on mineable planet
Mines and their requirements can't be built at all on planets that are not suitable for living: Builder Plant and Vehicle Plant are required for the Spaceport. Spaceport is the only way to add mining robots to mines.
You are left with the only single mining station per such planet.
Try focusing first on building the maximum amounts of mines (9) where possible on accommodable planets with required ores.