The AP story on that hot-air balloon altitude record (21000+ meters) said the balloon weighed 44 tons (2000-lb tons, I assume). That can't be right, can it?
At 21000 meters on a standard day air density is 0.075 kg per cubic meter, so 40 metric tons of air would fill a sphere 100 meters in diameter. So a 100-meter spherical balloon will lift 40 metric tons minus whatever the air inside the balloon weighs. We could figure that out, if we knew the temperature inside the balloon-- but surely the balloon couldn't weigh anywhere near what they said?