Originally Posted by Dr. Drib
Hal Clement's novels.
A very popular "hard" science fiction writer from the 1950s, who is very highly regarded.
If you decide to try Hal Clement, I would start with Mission of Gravity, which is probably the best novel he wrote. It is about a scientific mission to a high gravity planet.
I also second the Robert Forward suggestion. He writes books mainly about scientific expeditions to astronomically "interesting" regions.
You might like Vernor Vinge as well, as long as you stay away from his near future stories. Pick something like A Deepness in the Sky and you should be happy.
I'm suprised that you didn't mention Larry Niven. His Ringworld series should be up your alley, as should The Integral Trees and The Mote in God's Eye with Jerry Pournelle.