Courgette

Basically your entire application (GRE scores, transcript from your BS/MS years, letters of rec, and statement of purpose - am I forgetting anything?) need to show 1) that you're committed to coming back for your PhD and 2) that you're able to follow through on that commitment. You need to address both points in your statement, and you also want your letter writers to back you up in both points. The mechanical guy you worked with, if he can speak to your research ability, commitment level, etc, could definitely be a good reference, and the PhD he has certainly lends some credibility - but do try to get references from faculty as well - they are in general taken more seriously, especially from a well-respected institution such as GaTech.

you will need to write a clear statement of purpose succinctly describing your undergraduate and work background and how that has shaped your research interests and led to your choice to return for a PhD. you'll also want to take the GRE and score well on it (if you haven't already), because UT Austin is among the top for controls and aerospace, and make sure at least one letter of reference comes from a faculty member (better if more than one). while it is not the most common path to a PhD, your situation is far from uncommon.

it also varies hugely from institution to institution. big-shot profs at prestigious universities often don't respond at all - they receive emails from interested students on a daily basis and have other demands on their time. the advice I was given regarding emailing POIs was don't. You can contact them after you get in, but asking for their time before being admitted is presumptuous and annoying. worked out okay for me.

hi. I made an account just so I could offer my 2 pence on your question. I have very limited experience with applying to German institutions in STEM fields from American institutions, and moderate experience with the German university system. That said, I have been told that RWTH Aachen and TU Munich together are the best engineering schools in Germany - if your GPA is a 2.82/4 on an American scale, my sense is that is indeed below standard for those schools (unless you can say that by "above-average/good" you mean "top 5 percent"). Without knowing much more about you the most useful suggestion I have for you is for you to make use of your contacts at your home institution. Politely email a professor who likes you and ask if you can meet to talk about applying to programs in Germany. Ask what institutions he or she would recommend applying to and what your chances of being admitted are. Also ask if he or she can point you towards others who may be able to provide further assistance, advice, and knowledge. Odds are he or she won't necessarily know but may be able to connect you with other people in your department with greater experience - and through this network you may be able to find contacts at a German institution with a reason to take you on. lastly - look into the DAAD (German Academic Exchange Service) study grants for masters students.