20/02/2017, 8:20 PM · 29 replies and 589 views.
I'd say it's a-graded when every module is upgraded to the grade that is optimal for the total build. For an exploration ship, that might mean every module is d-rated or even lower class. For other ships it migth mean other grades are optimal. D-rated for life support and sensors is almost always the optimal build, no matter what you're aiming for. Some modules don't have "grades", so it just comes down to preferences.