Tom,
Thanks for all the details.
Are you sure that “diffuse.xyz *= diffuseLight;” was removed from all the shaders? It is still in the *FS.glsl files in the zip. When I comment it out, the solar panel shows up correctly, but the foil is still wrong (white in this case and some parts have incorrect texture coordinates) so perhaps it looks the same as the glTF Viewer?
If you know Blender, you can probably change the export options or materials to export something more friendly; given that the XCode workaround was needed, there was export issue. However, since the attached COLLADA file loads in Mac Preview, it should still convert to glTF OK. Submit an issue for the converter, which could also reference the diffuse issue (#231) that we see with these NASA models.
Patrick