This is full of in-jokes and parodies on other anime series. The entire "Aim for the Top" attitude and the science classes at the end are a parody on the school girl genre. Gainax went on to indulge their love of parody even more in the Mockumentary "Otaku No Video".

In the fifth episode when they give a close up of the Eltrium being constructed in orbit the construction gantry is actually sprue from polystyrene models (you can see gun turrets etc. attached to it if you look).

All the named moves and weapons used by the RX trainers and the GunBuster itself are pastiches on simliar things from series like Ultraman.

In the third episode Noriko teams up with a loner called Smith Toren. He is based on Toren Smith (Japanese put the family name first), an American who has been instrumental in bringing anime and manga to the US. I am informed this happened because Toren was staying with some of the people at Gainax at the time and they thought it would be cool to kill him off. Toren Smith also wrote the first few stories of the US Dirty Pair comic before the artist Adam Warren took over all the duties.