Maintain motion (no drag)

I'm trying to make a realistic space environment, I've got some fun results with low gravity and on and off levitation but not really accurate to 0g. I'm wondering if there's any way to have any entity that isn't grounded to maintain it's motion forever. essentially not have any drag. 
I've started playing around with seting the motion of the entity but it would require me to save the motion of every entity after it leaves the ground and constantly set it's motion to that value, which would end up needing to store a lot of values. And it doesn't work for players because it doesn't seem like you can modify their motion nbt.