So i've found a few really solid ways to stack up those nanites pretty quickly. The most reliable method ive discovered is finding those curious deposits, they look like these weird golden balls clustered together on planets. Once you spot some, drop a base computer nearby and set up a few short range teleporters, that way you can keep resetting them without the loading screens. The refining part is pretty straightforward, just remember its a 5-to-1 ratio when you process the mould.

If you're more into combat, taking on sentinels can be pretty lucrative too. They drop nanites directly, plus you get all these useful materials like pugneum and those shiny hyaline brains from the bigger ones. They also drop suspicious modules all technology merchants will happily take for big chunks of nanites. The radiant shards and inverted mirrors you collect are worth quite a bit when refined, which is nice.

Something that's been working really well since the interceptor update is the whole atlantideum thing. You'll need the minotaur with a decent laser to mine it effectively, but once you get the hang of the refining chain its actually pretty rewarding. Just remember you can combine it with pugneum to get even more out of it. Oh and if you're feeling brave, those abandoned buildings with the whispering eggs are worth checking out, just be ready to run when those biological horrors show up! The larval cores you get are definitely worth the hassle though, and setting up a base computer makes it easy to come back later.