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by namibj 2955 days ago
Apart from wind moving it to the side, it would not be a fundamental problem to fly a tethered blimp with a pair of single mode fiber and a thin aluminum wire that is driven in resonance [0] with the surface capacitance the blimp has, relative to earth, up to about 20-50 km. The breaking length of the fiber comes out at ~120 km, and you have to spare some tensile strength to hold the aluminum wire.

This is not hard, and for 8km height you could manufacture them for under $2k/piece. Even if they'd be made to work with hydrogen, as that raises the demands on the construction. If you'd find the FCC to be willing to allow something like this and are able to handle both thunderstorms and just the general wind load on the tether, this should not be hard.

[0]: https://en.wikipedia.org/wiki/Single-wire_transmission_line
1 comments
petre 2955 days ago
Lightning + aluminium wire is a problem. I suspect an electrical current will form in the wire even w/o lightning because of static electricity. Also the wire is a hazard if it breaks and falls down. It will probably cut everything in its path.
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namibj 2953 days ago
Yes, probably. Maybe you'd have to fly it at a place where you don't need to worry about lightning. But that seems rather restricting. Though, for high-bandwidth applications, it might then be necessary to fly local power, and have the whole system sit over the cloud layer, at about 50km.

Regarding the damage from it when falling down, you have to remember that each fiber weighs 50g/km, and the wire is also below 1kg/km, even for rather low heights. This should not be a problem, considering the ease of breaking an optical fiber optic at any remotely sharp edge. A small bird (the size your cat can catch) could probably snap it if he hit's it with some force.

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petre 2951 days ago
It will create a lightning discharge path regardless if you fly it over the cloud layer.

1 kg/km • 50 km • 9.8 m•s^-2 • 50 km = 24.5 MJ

10 MJ = kinetic energy of the armor-piercing round fired by the assault guns of the ISU-152 tank

I think that's just about enough energy to cut just about any living thing in half. Maybe it work if the cable was made of spider silk or Kevlar.

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