How did you put the two images together? I'm just curious because the outline of the ship is terribly jagged, and in my opinion really does detract from the overall effect. Being a bit more careful when "cutting out" the image of the spaceship to overlay on the background will help to "sell" the effect.
I have to admit I'm finding it hard to offer much more constructive advice or praise on the elements of the image that are by yourself, because to be honest all you've done is stuck one image over another. If you can tell us a little bit about your workflow then we may be able to improve your workflow and creative process.
