very nice mate. not sure if your going for realisim or not... but if you are then you have the sky the horizon in conflict with the view of the space scene... i spose it could be a very thin atmosphere, but then the horizon wouldn't be as opaque.
The lighting of the moonlet is off i think, though not 100% certain.
Over all though i reckon its kick ass. A fan-bloody-tastic composition guys. nice colab.