4.5 stars. This was fantastic. The audio narrator was wonderful; I'm so glad that's how I chose to read this book because truthfully my eyes would have glazed over from all the technical stuff if I was reading it. That science-y stuff is the main reason I can't give this five stars. Mark was an AMAZING, hilarious main character... because of him, I didn't want the story to end. All of the jargon was essentially impossible to understand but it didn't exactly dampen my enjoyment of the book. I looooved the flashes into NASA and what they were doing at the same time. That really made the book for me. I loved the foreboding feel to the book; I was always on the edge of my seat.. even when nothing much was happening. Can't wait to see the movie now!