What even is this book??? I am truly baffled by all of the 5* reviews. They must all be from people who have never read a drop of sci-fi in their entire lives, 'cos this. ain't. it. I wish I could enjoy, or even tolerate, such a poor-quality book. 
My first issue is with the memory loss - that's not really how memory loss works is it now? Remembering everything in chronological order and in full detail exactly when you need it? It just felt like a horrifically heavy plot device Weir tried to use to make the book more interesting/give natural info dumps to the reader, but in reality, it was the furthest thing from natural and felt so contrived that it took me out of the story at so many points. 
I was ok with the first 100 pages or so, and was interested while the premise of the book was being established, but by page 150 basically nothing had happened of note. We'd just been spoon-fed information in a 100% telling not showing, completely unnatural/contrived way. The (minimal) plot was dull and I started to get more and more annoyed with the whole thing. 
I also felt like I was being talked down to like I was an idiot for so much of it. e.g. "the model is Sol (Earth's sun)." - even if I didn't already know this pretty basic bit of information, it was BLINDINGLY obvious from the context. Not every single little detail needs to be explained all of the time!! Give your reader SOME credit. And every explanation of something is repeated at least twice and often more in as many pages...
The writing is also just pretty awful e.g. "The enemy of my enemy is my friend. If Astrophage is your enemy, I'm your friend." Shite writing. Unnecessary. 
After I decided to DNF, I skipped to the last couple of pages and the book had gone exactly where I thought it was going to. I'm glad any didn't waste any more of my precious time on it.