# What is the principle behind using a moment reference center to compute the moments acting on a spacecraft re-entering a planet's atmosphere?

I have seen the term "moment reference center" and from a general perspective, I understand that it is a point arbitrarily chosen to calculate moments acting on a entry vehicle (I am reading a lot on entry aerodynamics), my background is not in aerospace so I am trying to learn this on my own.

• This is a great question! In aviation, the Aerodynamic center is chosen as the pitch moment reference center because it makes the calculations much simpler: within the flight envelope, the pitch moment remains approximately constant relative to that axis. I wonder if there's anything similar for rockets. – Everyday Astronaut Sep 9 '19 at 18:57