I have tried different methods for rewarding. Now I reward the agent when it shoots while he is below the asteroid. However, before that I tried small rewards to encourage the agent to come below the asteroid. In final version, I removed them, because I could not get much better results by them.
And I have used PPO code provided in ml-agent package for training.
I would be grateful if you share your knowledge through comments about how it could be better.
If possible can you please post the code?