I’d love to know, too. If it was me I’d use a small piezo plate on the side of the balloon to do it the same way hot air balloons do. Heat the gas in the balloo

I’d love to know, too. If it was me I’d use a small piezo plate on the side of the balloon to do it the same way hot air balloons do. Heat the gas in the balloon = go up, reverse the polarity to cool it = go down. That would be pretty energy inefficient, though, so hopefully their secret method is better. Loon used pumps and an interior air ballast like blimps do. So clearly there are a few ways.