I think some light should be visible trough window's cockpit. Then overall illumination is too flat; in space you have big contrast between lighted and shaded part. There's no air or atmosphere so no diffusion light. When you reach your goal illumination with one side lit and the other completely dark you can help the model with some fill lights. Finally keep ambient value to zero and use instead of it a distant dark blue light for diffuse shading only or something similar. Hope this helps a bit
