Pictures from her dress rehearsal show the singer on stage accompanied by an astronaut and the flag, famously designed by artist Harold Thomas.
The typically camp (as is demanded by Eurovision) performance also featured a kangaroo/Socceroo, Koala and what looks like a hammerhead shark.
Mauboy sang Sea of Flags, a new original song, a snippet of which you can see below.
The second semi-final will take place on May 8 at 9pm (BST) or 5am on May 9 (AEST).
Images via Getty