I got a BS in Aeronautical & Astronautical Engineering from Purdue University, any suggestions on MS or pHD I should pursue?

What have you been doing since graduation? What's in demand in your country of citizenship? You are/were a foreign student? If so, you can only work in your country of citizenship. Since so much work for major aeronautical & astronautical companies is for governments, foreign workers can almost never get security clearances or visas. What did you go into this field for? What are your goals? Without more info, it's very hard to suggest anything but the obvious, master's in aeronautical engineering.