"Juvenile" science fiction novels are quite common. Heinlein wrote a whole slew of them, and Jerry Pournelle has a line of juvenile novels that he's attached his name to (I think).
I wouldn't recommend most of Heinlein's stuff anymore, although I think Space Cadet might hold up well as an adventure yarn.
Jerry Pournelle's Starswarm, Pournelle/Sheffield's Higher Education, Pournell/Niven's The Mote in God's Eye.
The Hornblower series.
Zelazny's Nine Princes in Amber.
Most of what Lois McMaster Bujold has written - the Vorkosigan series, the Chalion series, the Sharing Knife series.
Niven's The Integral Trees and The Smoke Ring (Looks like fantasy but is actually hard science fiction)
Frank Hebert's Dune
Timothy Zahn - The Blackcollar, the Cobra series, his Star Wars novels
Neil Stephenson's Cryptonomicon, and Anathem