OK, Here I Go
Well the first thing I am going to bust you on is the scan. You should have cropped it. As you have it at the moment it looks like you rushed it. Keep in mind that presentation is sometime crucial to the pieces survival So you should go ahead and crop out the rings, straighten up the angled right side, and airbrush out that mess in the top right corner.
Now moving on to the actual piece and trying to critique it.
I'm noticing a little of the under drawing still left on the page. Usually with a sketch that isn't that much of a problem, but I get the feeling that you are trying to pass this off more as a finished piece. I think you should adjust the the brightness and contrast a little, Try to get those little bits washed out. This will also help get your blacks of your inks to be a but more true to being black as well as the white of the paper more white.
You might want to be a bit more careful with the legs of the crewmate. His folded legs don't look like they are lead to his hips.
the captains right hand looks a little off. But with the position you have it is difficult to draw. Try changing the position of the hand and see if you get a better result.
Work on your line weight as well. And be sure to take not of how humans interact with there surroundings. Take the Captains foot for example, the toe should curve down a little more considering how the weight falls.
