MrFob9138: Here is the fastest way to make money I have found:
Build a Theta upgrade that require gravitino balls (e.g. the Plasma Cannon cooling system Theta). Now disassemble it. You will now have a stack of 5 gravitino balls, which allows you to stack them up to 100.
Now find a planet with with gravitino balls. Run around, and collect them (since you can stack them now, you should be able to collect a lot at once). If you have something like the personal shield upgrade Theta, you can just ignore the Sentinels. They may hit you a couple of times but they shouldn't be dangerous enough to kill you.
Sell you crap load of gravitino balls at some trading terminal for ~30.000 units each. This way, you can make a couple of million credits in an hour easily.
I managed to do this for neutrino modules (and thanks for the tip, it was very helpful), but I haven't got any techs that require gravitino balls. I don't even have a plasma cannon as far as I know. Are finding new techs just a matter of getting closer to the center? Because the past 200 or so techs I've found have been ones I already had. I don't recall when I last found something new.