We've got about a day and a half left and only 3 books fully nominated...
So, I'm going to lobby for a third for
The Calculating Stars.
This is a wonderful book with a diverse cast and is one of the few books to ever win the Nebula, Locus and Hugo awards. It is "science fiction" but almost all of the science is not fiction but instead based on the real space race of the 1960s, just accelerated a bit ("alternative history") and with more hanging in the balance than bragging rights for Russia or the USA.
If you want a preview (other than the Amazon or <insert store here> previews, you can check out
The Lady Astronaut of Mars at tor.com. This novelette, also a Hugo recipient*, was published several years prior to this novel but takes place afterwards (minor spoilers for the novel, I did not find them distracting) although the novel is better in my opinion.
*It actually nearly made the Hugo list the year prior to actually winning it. The previous year it had enough nominations to make the final ballot but the review team deemed it ineligible since it was published as an audiobook only at the time and it didn't receive enough nominations in
that category. It subsequently was published online and won the following year's Hugo.