[Nitrolo]

There's a concept in engineering called "Reißlänge" (≈ breaking length), which is how long a cable of a certain material can be before it would rip due to its own weight if suspended by one end [0].

The values for some materials are actually much higher than I remembered, with Kevlar reaching ~250 km. From a purely hold-its-own-weight perspective it seems like it might actually be possible!

Obviously there's a ton of other problems that wouldn't make it feasible, the first I can think of is the weight of a 50 km tether wouldn't allow the balloon to even take off. I'm sure you can think of another million reasons it wouldn't work.

[0]: https://de.wikipedia.org/wiki/Rei%C3%9Fl%C3%A4nge

[lovemenot]

That's interesting and surprisingly long for Kevlar.

The highest altitude recorded by a single kite is less than 5km. I understand the biggest constraint for higher flights is tether strength-to-weight ratio. Nylon is typically used - fishing line.

Tether diameter is another factor as the load from wind, on the tether alone, is considerable over such lengths.