First I would like to say that I am a sucker for sci fi and that I am absolutely loving your work.
Now for the Critique:
The darker and deeper colours in the left bottom combined with the brighter and lighter colours top right give a good balance. Overall your composition covers the basics nicely. The colour scheme is very natural and greatly ads to the dynamics of the piece
The dynamics are nicely done. There is a lot of depth due to the detailed astronauts and terrain in the front and the more sketch like facility and background. The glow from the lava pit on the rig is also adding up to a more dynamic environment together with the smoke and hot ash.
The perspective however is not as good as it could have been. My guess is that you work with a free interpretation of perspective, which is fine but can be very risky. As a result of your experience, it still looks fine especially with all the complex shapes and things that stick out from the rig, which mask it's odd lines. In the end, it still looks a bit crooked to me.
I also believe that she shuttle could have been done a bit better. Perhaps with some more pronounced shadowing. It kind of disappears into the grey background
All in all a nice piece of work. I really like the design of the rig and the the two dudes in the front are awesome.
Astronaut one - "well, there goes the annual ice cream truck. I bet they didn't leave any for me... sure could go for some ice cream right now... you know, with all the heat, lava and.."