> not that I know if half density is a feasible figure 1/15th - .08 kg/m^3 at 20km, 1.2 kg/m^3 at sea level. 20km is way the heck up there. And yes, it does ma

> not that I know if half density is a feasible figure 1/15th - .08 kg/m^3 at 20km, 1.2 kg/m^3 at sea level. 20km is way the heck up there. And yes, it does make it difficult to build something buoyant enough, which is why the use case for this is something like a geostationary internet balloon rather than for transportation. https://www.engineeringtoolbox.com/standard-atmosphere-d_604.html https://www.engineeringtoolbox.com/standard-atmosphere-d_604...