the question that arises is why an ufo with a gravity engine should need breathable fluid antig
i think its due to terminal velocity:
propelled by earth g force on free fall in a plane at the begining you feel zero g on your body everything fine
but on reaching terminal velocity you feel a whole one g
so if youre propelled by a 1000 g thruster in the beginning you feel zero g but once reached terminal velocity(in any atmosphere) you need being sink in antig breathable fluid or youll feel those 1000 g becoming a bloody mass
the things is that this ufo have to be combat ones
ihave had vivid dreams of being in ufos in which you have to hold yourself to something when it jumps to interplanetary speed