Apparently a fuel pod; who knows. Its a CAD model of the basic geodesic dome without the inserts at each triangle.
This is modelled in CAD as close as I can get to studio scale based on a couple of photos on the Lunadude website that has a rule alongside.
A classic science fiction spaceship from an absolute classic sci-fi movie; one of the best. The original prop was a massive thing and is interesting to read about; the side length of one of the hex / triangles is 3" (75mm) long.