The book before I started to cut.
I wanted the stairs to spiral, so I drew one using the Fibonacci sequence. It works well, if you need a quick, accurate spiral.
I also wanted the stairs to be evenly spaced and radiate out from a center point. To do this I divided a circle into 1/6ths and subdivided this twice more to create the above drawing. I made all the drawings on tracing paper so I could overlay the designs for the final one below.
Here is the piece of tracing paper I used to make the cuts in the book. I first traced the outline of the boy and asteroid that I wanted to keep, then I added the spiral and the radiating lines from the drawings above.
This picture illustrates how I cut each section of the stairs starting at the back of the book and cutting larger wedges as I went.
Here are the tools of the trade that I used during the process: a thin cutting mat, two exacto knives (one for straight lines and one for curves), a 1/4" spacer for the page edges, and a pencil to trace the lines from the tracing paper onto the book pages.