AstroGodzilla's name comes from the prefix astro, referring to space, and Godzilla. This name is used to refer to the monster in an article on the unmade film in G-Fan magazine. Some concept art for the SpaceGodzilla predecessor instead refers to it as "CrystalGodzilla."
AstroGodzilla, being a prototype for SpaceGodzilla, shares many similarities in appearance with him. Each of AstroGodzilla's concept sketches loosely resembles Godzilla and possesses crystalline growths on its body and tusks around its mouth.
However, many of AstroGodzilla's sketches look noticeably different from SpaceGodzilla. Some of them possess additional limbs or massive dorsal plates that act as wings. Several possess either forked tails or two separate tails.
AstroGodzilla, spawned by some of Godzilla's cells brought into space by Biollante, comes to Earth with an army of giant alien dragonflies in order to conquer the planet and kill his earthling counterpart. AstroGodzilla sends his dragonflies to Birth Island, where they attack Little Godzilla.
Godzilla arrives to defend his son against the dragonflies, but AstroGodzilla uses his telepathic powers to take control of Little Godzilla and Miki Saegusa's minds and force them to do his bidding. When AstroGodzilla invades Japan, Godzilla joins forces with the G-Force mecha M.O.G.U.E.R.A. and Mothra to stop his extraterrestrial clone and save his adopted son.