It's not quite that simple. So many factors, as well as random chance, affect the quantity of TEA/TEB used that it's virtually impossible to create an accurate prediction. Other comments in this thread mention that they could probably have modeled and tested on the ground until they had a better idea, but that takes a long time and is expensive. Actually launching the thing and learning from that is a much more effective usage of time and money. As someone else ITT quoted George Box "all models are wrong, but some are useful.".
