i am a rather hardcore Sci-fi fan, and have also read several of clarke's books(Rama series) i like science fiction vs fantasy. i guess it would fall into a Hard Sci-fi role, storys based around hard facts.
"Planetes" (space) is a good example of a hard sci-fi anime.
"Patlabor" for mecha.
"Yukikazi", for aircraft. but they are rather few and far between.
even "full metal panic", with the exception of the Lambda Driver...
i do enjoy a good Science fantasy, Last Exile, nadesco, cowboy bebop,etc...the ideals that they come up with are great to watch, and make for wonderful worlds. sure trying to bend them to match our science is impossible but it makes for a good show.
and Clarke is a good read for sci-fi fans...really should get around to reading 2001 again...and Rama