Writing and talking about a subject helps you crystallize what you already know and it points out what you don’t yet know. Explaining something to another person also explains it to yourself and helps burn in the learning. Niels Bohr once said about a sea voyage with Albert Einstein (paraphrase): Einstein explained his new theory to me every day of the Atlantic crossing; by the time we reached New York, Einstein understood his own theory. If someone as smart as Einstein can figure out a tool like this to master a subject, don’t you think that it would be wise to consider it too?
Clearly, just explaining something, over and over, can get pretty boring (I don’t envy Bohr on that voyage). So, in an effort to avoid tormenting your friends and loved ones (which I try not to do unless it is on purpose), write stories about the subject. That will be much more fun for you and everyone around you.
Knowing what you don’t know is very difficult. In writing a story, you get into situations that require information that you don’t have and the characters (if done right) will have different perspectives. The characters themselves may try things that you don’t know how to do. Then you get to figure out how to do them. Think of how much you will learn researching space travel for your stories.
If you are wondering what kind of science fiction to write, you can start with what you like to read or what you would like to read if you could find someone else writing it. GURPS Space is also a good source of ideas. GURPS, in general, is a font of information on a variety of subjects.
How can a gaming supplement help you write a story? Their source books have a lot of useful information on their subjects that isn’t just useful for gamers. Remember that a role playing game is just a form of narrative in which the other players control the main characters of the story. In the first few pages, GURPS Space talks about the distinction between hard and soft science fiction, the scale and scope of the environment the story take place in, tone, and story types. They talk about two different types of realism: scientific and social. For the type of story we would write for space travel, we would want to keep scientific realism pretty high (often with some rubber science FTL drive). But what about social realism? How important is it that the society makes sense? Does it follow the rules of political and group dynamics?
They then go on to talk about different plot types: High Frontier, Planetary Romance, Mercenaries, Heroic Engineering, etc. Aside from discussing the various types, they also give: character roles (pilot, tourist, bureaucrat), things to do (scrounge resources, build a radio from coconuts, navigate near gravity sources), plot advantages (what are things that are easy/enjoyable about this type of plot), plot disadvantages (what do you have to watch out for with this type of plot), and references (those guys always have lots of references).
As you can see, a lot of work goes into the GURPS books and you can get a lot of value from the book before it starts to get into game specific information. You could do worse than using GURPS Space to build your starships and characters. They would then all follow the rules you set up for your story.
*Most anyone can do this