I think it's really hard to come up with a completely general breakdown of something like this - the way you break it down is biased by your interests. For example, I noticed that Ari Jokimaki's breakdown is based *mainly* on categorizing topics by location. Since I'm an engineer, I would be tempted to expand technology/missions into multiple categories and cram Ari's topics 3-5 into one topic.

Another way to organize it might be roughly by science field. But then, that's because my background is in science :-)
For example:

"Engineering" - technology and space missions
"Physics" - theories about the nature of the universe, relativity, etc.
"Astronomy" - categorization & study of celestial objects, past and present
"Biology" - astrobiology
And so on...

I realize that today everything is so interdisciplinary that you can't really describe these fields as black-and-white as they appear above. I'm just using the stereotypes of the fields as a sort of thought experiment.