Facility:
Mining Hub. When placed on a planet, it will send out small automated mining vessels (mechanics could be similar to mass driver packets, just for fluff and looking cool) to nearby (1m km, upgrades with engine efficiency tech?) asteroids and small moons, slowly harvesting their minerals at a set amount per year. Could scale with the mining techs.
Module/mechanic:
Laboratory module. Make it huge, expensive, crew-intensive and heavy, but I've always wanted to make science vessels. There must be heaps of discoveries waiting to be found in those new star systems, considering the breakthroughs we already made with our limited space exploration IRL. It could allow for a new mechanic, where some planets can spawn with a pool of 'research points' in a specific field. A science vessel could perform research near the planet, then return and offload those research points into a tech currently being researched.