Some things from the book that I recall:
Rocky survived as engineer because his quarters were near engine, thus surrounded by astro****e that doesn't let any light/radiation to pass. His crew mates were exposed and succumbed to radiation.
Hail Mary was designed with a thin layer of astro****e in hull to protect crew from rads.
Grace named astro****e in the book, the President called it by name in his national address that same night.
When they captured the taumeba and lost 3 fuel tanks, all the fuel was contaminated. Generator went down first causing a life support issue. Problem had to be identified and then solved, ship cleaned.
They had to use 3 of the beetles to propel the HM back to blip a, leaving only one beetle to send back to earth.
As stated, the science behind communication was amaze amaze amaze, as well as the base 6 eridian math.
Rocky converted everything into earth time for Grace, exceptionally fast with calculations. Extremely talented engineer.
After splitting up, Grace used his petrova scope to check in on Rocky every day. He realized the problem with xenonite and taumeba after about 30 days. His method to find the blip A was super methodical and well thought out. Lots of math, and trial/error. Him finding the blip A was extremely satisfying and the reunion was very emotional.
Grace realizing he was a coward was really well done in the book. He knew turning around to try to help Rocky was death, after he just received a new chance at life. It was so compelling how he chose to sacrifice himself for Rocky, not for Erid or even the Eridian race, but for Rocky. He refused to sacrifice himself for earth and the entire human species, but he laid his life down for Rocky.
Some of my favorite parts of book were when they were hypothesizing how they can hear similar frequencies, the odds of both of them being there at same time, similar level intelligence, just overall similarities of two beings from so far away. Andy Weir has a fascinating mind and those conversations were very thought provoking but also very developmental and foundational to their friendship.
