>>jnord+(OP)
I wish the regulations around HAB were not so lighter-than-air gas centric. Hot air balloons are much more accessible, especially solar heated hot air balllons. But they have much less lift per volume and so the FAA FAR 101 rules basically say they all have to be treated as the type where you inform the FAA beforehand and then every hour about their position among other things.
https://www.ecfr.gov/current/title-14/chapter-I/subchapter-F...
>any balloon that is moored to the surface of the earth or an object thereon and that has a diameter of more than 6 feet or a gas capacity of more than 115 cubic feet.
And the regulations on tethered balloons end up being even stricter than letting them go.