Very interesting concept you got there.
When playing, i actually think it was easier never to let go of the astronaut and always tried to avoid the asteroids. That was mainly because if i let go of the astronaut, the oxygen loses and no longer regenerates. If the astronaut would regenerate oxygen, you would encourage the player to let go of the astronaut sometimes. Then it would be more of a rewarding mechanic than a punishing one.
The overall presentation of your game looks really smooth. Good job on that.
All in all, i think this is a pretty polished and well made submission. Great job.