It looks like once you've finished researching all available technologies up to tech level 50 in a specific category, you are presented with a set of Advanced Something Tech I to X to research.
The in-game description for all these levels reads: "General improvements of existing something technology."
I couldn't find any answers on the Internet, and I don't notice a difference in the speed of ships with Advanced Propulsion Tech I.
Does anyone have information on what it actually does? Is there any actual advantage to researching it?
(You can see a full technology tree here: http://www.moo3.at/moo1/technologies.php)