Astronaut’s Grave – Death row prisoners are given freedom by the state if they can come back alive from a space exploration.

Perhaps a few whys? Answered

Why use death row inmates?
Why is it so dangerous?

Worry about the main character issue once you can article the conflict.

Hello, Jlmarvevalo.
Thanks for sharing your logline. Is there a main character that the story focuses on? That would help to make the longline more specific and compelling. I'm assuming your character is one of these prisoners. Why will we care about this particular character's story? Is the person a murderer? Is the person innocent? Is the person afraid of flying? Would the person rather stay in prison? Does the person actually want to die in space? (Am just tossing out some ideas. You may already have the answer.)
Cheers, SouthWestSusie