When I read the brief title I did not know the end game was space travel. If you stay put on mother Earth I suggest ME and if you can take your electives or extra classes in Aero do so.
I had similar thoughts years ago, leaning towards Aero. But it hit me one day, post Apollo Program, that it may be better to go ME. I was not that smart then and think is was a message from above. Roll forward a few decades and my decision was a good one. Right or wrong, everyone hires ME's not so for Aero. Abilities, skills, training for the most part can be equal, there is a stigma that Aero's work in programs with infinite amount of government money and other conditions that don't lend themselves to commercial work. I have been away from corporate life for 10 years, but that was how I saw it for 30 years prior.
As far as space flight that is a guessing game for you this far in advance but a good time to start. First, if you have any health issue that may disqualify you from among thousands that apply, be honest with yourself. Next who is hiring? NASA seems to be getting out of the business. For the Mercury Program jet pilot was the entry ticket. Now NASA wants PhD in science for crew. For the commanders they may still want military pilots, if they are in the business by the time you are ready.
If space goes private determine who will be doing it (Musk for example) and inquire what they want. A mechanic to keep the ship running to and from Mars?
Good luck.