My son is a junior at Texas A&M and wants to get a PhD in aerospace engineering, focusing on plasma rocket propulsion. Last week over his spring break he flew to Atlanta and met with the professor who runs that program at Georgia Tech. It was an informative meeting, but one thing he learned was a surprise. Most every school requires three letters of recommendation, with two of them from a professor who can discuss your research. For aerospace engineering, all three letters must concern the applicant’s research. That’s not the case with all departments. So, it’s a good idea to check way in advance to see what the department’s specific requirements are before it’s too late.