The Theme of the One-Way Mission
Project Hail MaryThe Hail Mary is a suicide mission, and the crew accepts their fate.
increasing
Bearing strength in each event
decreasing
The Volunteers

The Willing Sacrifice
The Astronauts' Choice
Yao, Ilyukhina, and DuBois volunteer for the suicide mission. They know they will never return. They are heroes in the truest sense.
The Personal Reasons
Each has their own reason: DuBois wants to contribute to science, Ilyukhina wants to die with pleasure, and Yao wants to serve his country. They are all ready to die.
The Contrast with Grace
Grace is forced onto the mission. His journey from involuntary participant to willing sacrifice is a central arc. The theme explores the nature of sacrifice.
The End of the Mission

The Final Act
Grace's Decision to Stay
Grace could have gone home, but he chose to rescue Rocky, knowing he would likely die. He accepts his fate. The mission is no longer a one-way trip for him, but he is willing to make it one.
The Survival
Grace survives on Erid, but he never returns to Earth. The mission ends with him living in exile. The one-way nature of the mission is fulfilled in a different way.
The Legacy
Grace's story is a testament to the idea that sometimes the mission is more important than the individual. The theme of sacrifice is complete.
Before launch
After the beetles are launched