Some people are so nitpicky...
From TFA: "He instigated a top-secret experiment, code-named Project Mogul, that sent up hot air balloons equipped..."
I believe this is an error. Per Wikipedia [1]: "...rubber meteorological balloons, however, these were quickly replaced by enormous balloons made of polyethylene plastic. These were more durable, leaked less helium...". So the Project Mogul balloons were NOT hot air balloons. Which is not surprising. To fulfill the mission, a hot air balloon would have to carry fuel and perform controlled burns to maintain altitude. Not that this would be impossible, it is just easier IMHO to release ballast.