Well, while I'm not finished yet, I'm currently reading Encounter with Tiber by John Barnes and Buzz Aldrin, and it's really very good. I love Neal Stephenson, and I love books that have a bit more to them. And Encounter with Tiber is right up there, according to many reviews I've read, with some of the best hard sci-fi and sounds right up your alley. It gets right into the science aspects in a spectacular way, right down to drawings to explain some of the concepts. And it's a rather ambitious novel. Amazon just recently re-released it for the Kindle, as it was originally published in 1997.