I was looking through some old pulp magazine covers and came across these two images that gave me quite the Death Star vibe.
The first one is a reprint of H.G. Welles The First Men in the Moon and the orb is only a few meters across, however in this cover art it look gigantic, like its looming over the lunar surface. I wonder if Lucas might have seen either of these and been inspired.
Amazing Stories Volume 02 #11 (1928)
Amazing Stories Volume 07 #07 (1932)