What do you mean by MEC engineering? Do you mean mechanical engineering? Artemis program would not only have lots of engineers working on it, but many physicists as well. You can be either an engineer with better understanding of the underlying physics, or a physicist/astrophysicist with an engineering background.
Even though some colleges may offer it, there’s really no such thing as an undergraduate degree in astrophysics. As another poster has said, you need a graduate degree. To get into a good graduate program, having taking the right courses and ideally with some research experiences in relevant areas are more important than the major and/or minor you’re in. Unlike undergraduate admissions, admissions to graduate programs are decided by professors in the field, who are able to and will look into the specifics and granularities in your preparations, not just a few names on a piece of paper.