Welcome to the forums :)
I really like what you are going for here.
A few tips though, the blue space ship is a bit confusing as to what direction its facing. From behind I feel that its facing away from us and going towards the city. But when I look at the front it looks flat and seems to be going towards the right side of the picture, so clear that up a bit, and the shading on it is very black. You should paint with more values. The furthest part of the ship should be a little lighter than the part closest to us.
Also on the right side of the picture closest to us, there´s something white, another ship? ice? Its really hard to tell. When drawing stuff its good to hint at something and then let our minds fill out the blanks :)
I hope that I didn´t confuse you too much.
Overall you did a nice job :)