The Spaceship Moon Theory, also known as the Vasin-Shcherbakov Theory, is a pseudoscientific theory that claims the Earth's moon may actually be an alien spacecraft. The theory was put forth by two members of the then Soviet Academy of Sciences, Michael Vasin and Alexander Shcherbakov, in a July 1970 article entitled "Is the Moon the Creation of Alien Intelligence?".
Vasin and Shcherbakov's thesis was that the Moon is a hollowed-out planetoid created by unknown beings with technology far superior to any on Earth. Huge machines would have been used to melt rock and form large cavities within the Moon, with the resulting molten lava spewing out onto the Moon's surface. The Moon would therefore consist of a hull-like inner shell and an outer shell made from metallic rocky slag. For reasons unknown, the "Spaceship Moon" was then placed into orbit around the Earth.
Spaceship Moon Theory on Wikipedia
Who Built the Moon? - An Interview With Christopher Knight
The Death Star is a fictional moon-sized space station and superweapon appearing in the Star Wars movies and expanded universe. It is capable of destroying a planet with a single destructive beam emitted from the large indentation on its surface. (Wikipedia)