Hi Michael T
There is a little problem with SU Exporter for OpenSpace3D
You can't explose a scene with some objets From Sketchup so you must import one by one !

So best if you have object multiples : Moi (obj) --> Blender --> OpenSpace3D
or Moi (SKP) --> SKetchup (Collada) --> Blender --> OpenSPace3D ;)