Originally entitled Godzilla Vs. Astrogodzilla, the original storyline featured a rather ambitious callback to the beloved Showa era. Astrogodzill is the product of Biollante's cells drifting off into space. No doubt on this part of the Demon of the Depths origins this time. Astrogodzilla is an albino daikaiju. He possessed gigantic wings with which to fly, two long tails. And also to symbolize his polar opposite nature to the original, Astrogodzilla could fire a freeze ray from his mouth which could instantaneously freeze anything it hit. Upon Astro's arrival to Earth, the space monster psychically takes over the minds of Little Godzilla and Miki Segusa. Forcing the two into doing his bidding. Godzilla goes to Japan to fight Astrogodzilla, and free his son from the demon's clutches. He teams up with MOGERA, and Mothra, then a freed Little Godzilla to do battle ,and stop Astrogodzilla's malevolent plans in their tracks.
However due to Toho's big fantasy epic ,Yamato Takeru bombing, the studio got a little bit skittish on spending. The flick's budget ended up getting slashed, and Astrogodzilla became Space-Godzilla, with a more run of the mill plot. MOGERA almost went to the scrap heap to be replaced with a return bout with Mechagodzilla. But the bird beak mecha was put back in for the final flick.
Another thing left out, which I thought was apropos. Was that Astrogodzilla, being an indirect offspring of the King of the Monsters himself. As royalty, he was to have his own subjects. A swarm of alien dragonflies that did Astrogodzilla's bidding.
Finally, here's some concept sketches that show, what might've been the look Astrogodzilla have been sporting in the flick, had not Toho had gotten a severe case of cold feet.
:mechagodzilla: