The Saturn image was in the background and would not reflect toward the foreground viewer. So I reused the background starfield and mapped it onto the surrounding environment so that it would be reflected by the helmet glass and any metal on the suit. With this done, the face was the next area to focus on. I hate hair in 3D, because the geometry is so complex, and the fluffy surface of hair is not directly available in 3D. I made a first cut at the shape and texture - and then decided to try various compositions. Each rendering takes an hour or more, even without cast shadows.
Cast shadows are much more expensive in rendering time.
Posing the figure in front of the backdrop for maximum effect is the key difficulty at this point. It is possible to make decisions with fairly crude renderings. Once a satisfactory result is obtained, the detailed rendering is done. It became clear that the image of Saturn was not going to work in the original orientation, so it was flipped vertically. That somehow seemed to guide the eye much more smoothly through the possible compositions.