These things look like they’re a hundred feet tall and severely underfilled. Wouldn’t it be better if they were squattier like normal balloons and filled all the way? This question dawned on me while watching the guy who had broken a high altitude record and parachuted to earth. Wouldn’t he have gotten a few extra feet for his record if his gondola hadn’t been so far beneath the balloon itself?
It’s a pressure thing. As the balloon rises the pressure outside the envelope drops, so the gas inside pushes out to occupy more space.
The balloon looks so tall and empty on the ground because it has to be able to accommodate the inflation of the gas it contains as the outside pressure drops. If it didn’t it would probably burst, which would be a bad thing.
Like he said…
At low altitudes the balloon looks like a potato in a sock (If potatoes floated in air and if socks were made of mylar.) As the balloon rises, the gas expands and the dangling part of the balloon fills up with gas.
Now the balloon would look much more conventional.
At some point, the outside pressure can get so low that the gas expands to a point that the balloon pops. Then it is a one-way trip back down.
Fine answers! Thank you both!
This diagram shows a balloon at launch vs. at float altitude. Also here is a photo of a balloon at float altitude, most likely taken through a telescope.
By the way, high-altitude balloons usually do not pop when they reach float altitude. There is usually a hole in the bottom to release excess helium, so the altitude stabilizes at some point.
Since the gas does have an escape route, I assume one could completely inflate the balloon at launch time without danger of bursting, but it would cost more in helium, and the only conceivable benefit would be a faster ascent. And that might be harder for the systems and people aboard.
If you try to fully inflate the balloon at sea level, it would produce so much lift that the balloon envelope and/or the rigging will break immediately.
We’re not talking about a slightly under-inflated balloon here. Even at a modest altitude of 30km the pressure is 1/100 of sea level, so if you fill up the balloon by 1% at launch it will fully expand at 30km altitude. For a 40km altitude, it’s more like a factor of 500.