3 in 1 (parameterised)

This is an extension of my recent upload (of a coin in a sphere). This time with a small sphere inside a larger sphere inside a larger sphere... I stopped at a total of three.
You may have noticed that the large green sphere is a little smaller than the large red sphere and I've uploaded stl files for sphere 1 of 3, the smallest through to 2 variants of sphere 3 of 3, the largest.
I've also uploaded an scad file. The design is fully parameterised and comment heavy so it should not be difficult to generate your own spheres.