Clicking the links on the left of this page may well answer a lot of your questions:
http://www.defencejobs.gov.au/airforce/jobs/AerospaceEngineerOfficerElectronics/Entry/?entryTypeId=3
However you'll need to be
exceptionally good at mathematics to succeed in that field. (My own university degree is in mathematics, and I've taught maths to university entry level, but I know that I'd still find much of the course content for a subject such as Aerospace Engineering to be extremely difficult).
Given your high IQ, you would probably perform well in the written component of the aptitude tests:
http://content.defencejobs.gov.au/pdf/triservice/DFT_Document_GuideToAptitudeandAbilityTesting_20090810.pdf
but it has to be faced that the ADF might regard it as a problem that you state "I'm very inarticulate" since good communication skills would seem to be an obvious requirement for a military officer.
Your best chance of getting meaningful answers though is almost certainly to speak to someone in the ADF recruitment team. Phone 13 19 01.
Incidentally, you might be 'doing yourself down' by describing yourself as 'inarticulate'. Psychiatrists and psychologists can never agree as to whether my own position on the autism spectrum actually falls within the definition 'Asperger's Syndrome' or is only 'akin to Asperger's'. However I'm certainly lousy at communicating within most social situations but rather good at communicating elsewhere (such as in a classroom). The wording of your post (which is far from inarticulate) suggests that something similar might apply to you.