Mission of Gravity (and, if you like that, its sequel Star Light).

Hal Clement was very nice to me when I started out as an SF writer. So I should get my hands on that, if for no other reason.

By the way -- Bill Lindblad, the bookseller at ALIEN MOTIVES, keeps an eye out for my books, and does not sell them at a huge markup. You could tell him what you're looking for, and see if he has it. He's at amotives AT hotmail DOT com.