Good astronomy and physics... Methuselah's Children and Time for the Stars are the two that come immediately to mind.

Good science for the time it was written (when we had not yet discovered much that we know now) would apply to virtually ALL of RAH if I recall correctly. The biggest stumbling block is achieving velocities beyond c, and that is a problem if you are going to postulate any interstellar travel, (except generation ships) and does not even touch the more pressing problems we face in the real world of interplanetary travel, especially radiation during the voyage. BUT, on the whole almost all of them seemed to be at least better about accurate science than others of their day.

We also need to keep in mind that his stories were about people - ordinary humans (well, Heinlein heroes anyway, but the DNA was at least similar). I think the science was a vehicle to stretch the minds of the readers and pour a new concept or two in while it was still open.

Even Blowups Happen and Roads must Roll were plausible. Lifeline maybe not so much....

Nice to see you back, Audrey.

I just finished the nth re-reading of Blish's "Cities in Flight" and the level of scientific detail in there - dealing specifically with FTL among other aspects - is both gratifying and mind-boggling. Blish didn't do things by halves. The detail - down to the equation level - is so deep and echoes so many familiar (to my eyes) terms that when I was in school I spent many hours in physics textbooks trying to figure out whether his antigravity description could be true.