I think this ‘depth shading’ challenge is too difficult for students who use a pencil and paper. Shading an A4 paper, being dark for the most part is never even in grey values. While digital you can choose from 0 … 1 between black and white. Impossible for pencil and paper.
This is not a big problem while creating simple objects, spheres, cubes, chests. But a whole scene like the space scene is a different magnitude.
80% of this illustration, must be in a tint of grey (A4 paper size) to create the illusion of depth.