What is a good minor for students in aerospace engineering/mechanical engineering?

Some sort of communication degree. Especially of you work in a team company, if you can't communicate well with presentations, electronically, or to superiors properly, it's hard to continue if they don't understand or misunderstand you. If its not covered in the major, look into computer science or repair, as I'm sure you'll be using a lot of computers and networking with you work that way you'll be able to use those with out having to ask and repair your self if you need to. Plus it's a good fall back job if for whatever reason your first one doesn't work out. Good luck

I would say pure mathematics, or some other form of matematics, and computer science. Anything that could be somewhat relevant to your future course and/or career would be beneficent. :)