Thank you for your replies, it has been usefull. I changed the size of the particles, their speed and their rate, and also set my emitters in directional instead of omni, it's much better.
I tried to give a little more weight to my landing sequence by droping the robot more off.

It's rendering right now, I'll post the masterLayer render when it's done. And then I'll be ready for the ambiant occlusion layer