After PhD in Aerospace Engineering, could I be admitted into a top university for a second PhD in Computer Science?
A major part of doing a PhD is learning how to do research and handle working on problems which sit on the edge of what is known. You've done that already. Doing it a second time is unnecessary, expensive and time consuming.

If you've been doing aerospace engineering then you almost certainly have the necessary calculus under your belt already. And if you have a PhD you can teach yourself stuff. Buy a few good textbooks - I recommend "Pattern recognition and Machine Learning" by C.M. Bishop; "Information Theory, Inference and learning Algorithms" by D.J.C. Mackay (this one is free to download on the author's website because he's nice like that). Look up material universities and other insitutions put online - e.g. https://www.coursera.org/course/ml is a free course, whose description sounds like it covers a lot of the necessary basics.  A lot of machine learning conferences make their proceedings available for free - ICML and NIPS I think both do this, and the work is good quality.

Start getting up to speed on all this stuff. If it still interests you and you want to go the academic route, go looking for postdoc positions and then try to find a couple of talented people you can form a startup company with.