Who is Ryland Grace and what’s his mission in Project Hail Mary?

Ryland Grace is the protagonist of Project Hail Mary. He wakes up alone on a spacecraft with amnesia and gradually recalls that Earth is threatened by Astrophage, a microorganism that is draining the sun's energy and causing a global crisis. His mission is to travel to another star system, Tau Ceti, which appears resistant to Astrophage, to discover why and find a solution that can save Earth before it freezes. Along the way, he teams up with Rocky, an alien engineer, and together they work to breed Astrophage-resistant organisms to stop the threat.