Rama II by Arthur C. Clarke.
By the way, if you are a Scifi fan and you like authors like Clarke, Asimov, and Heinlein - who would you recommend from among more modern scifi authors? I am about to read "The Martian" by Andy Weir after I complete the Rama series. I enjoyed the movie "The Martian" and I am ready for something new.
You might also try Alistair Reynolds - "Revelation Space".
Also "The Expanse" series by James S. A. Corey, first book is "Leviathan Wakes"