I'd guess booster rocket from the corkscrew, but your 750k's* plus from Woomera(WPA). I know they have been active recently as they made the news when they managed to damage some heritage sites.
Just had a quick search, Port Lincoln is currently being used for rocket testing, that would put you in the right direction and within testing.
https://www.abc.net.au/news/2022-02-...-way/100847764
*Kingston SE?