MakerBot Print is our newest print-prepration software, which supports native CAD files and STL assemblies,
allows you to interact with all your printers via the Cloud, and many other exciting new features.
If you look at the cross section of the model (7th image), you will see that there is a 0.2mm gap between the base and the outer sphere. If you slice with a 0.2mm layer thickness, you should find that in the preview of your sliced output, there will be exactly one layer where the outer sphere is not attached to the base ring. In reality, the outer sphere will end up weakly fusing to the base ring, but can easily be broken free by prying inward with a screwdriver. (Note that I am talking about the vertical gap between the outer sphere and the base ring, not the horizontal gaps.)
However, if you slice with,say, a 0.3mm layer thickness, the slicer may not detect the small gap and will fuse everything solid.