Andy Weir. Project Hail Mary.

Science fiction. Set in the near future, it centers on school-teacher-turned-astronaut Ryland Grace, who wakes up from a coma afflicted with amnesia. He gradually remembers that he was sent to the Tau Ceti solar system, 12 light-years from Earth, to find a means of reversing a solar dimming event that could cause the extinction of humanity.

The story follows two storylines, each told chronologically, starting with the story on board the spacecraft Hail Mary where Ryland Grace regains his memory in bursts. This story is frequently intercut with flashbacks revealing earlier events leading up to the launch of the Hail Mary.