Ukrainian Drones With Fibre-Optic Cables Have 41km Range

Messy napkin maths to explain this to myself, because it is wild to me that 41 km of anything fits in that. I will use the top picture and assume that the guy's hand is about the same size as mine; my hands are reasonably large, so this should err on the safe side, and his hands are at a similar distance from the camera to the spool. That gives me a very approximate scale of 2 pixels per millimetre.

Diameter of the spool case: 365 px = 183 mm = 0.183 m Radius of the main section of the case: 91 mm = 0.091 m Length of the main section of the case: 477 px = 239 mm = 0.239 m

Volume of a cylinder = pi r r l v1 = pi * 0.091 * 0.091 * 0.239 v1 = 0.00622 m^3

I will assume that the shaft of the spool is the same diameter as the narrow part of the case

Diameter of the spool shaft: 55 px = 28 mm Radius of the spool shaft: 14 mm = 0.014 v2 = pi * 0.014 * 0.014 * 0.239 v2 = 0.00015 m^3

Subtract shaft from first volume = 0.00607 m^3

I'll assume that the cable has the same volume, as if the case had zero-thickness walls and the cable filled the case perfectly. Since the cable has the same volume, dividing that volume by 41,000 m should give us the cross-sectional area.

0.00607/41000 = 1.48e-7 = 0.000000148 m^2

Square root of that to get the length and height of that cross section = 0.000345 m = 0.345 mm

This number can effectively serve as the diameter of the cable, since it'll have a circular cross section. And... yeah, I can find 0.25 mm diameter optical fibre easily, so the numbers check out.

From what I've seen, they cost around 1-2k Dollars for 40 kms, probably cheaper if you buy in bulk. A single spool of 125 µm fiber weighs around 3 kg but half of that is probably the spool itself.

Probably pretty reusable as well

That's impossible. How can it be that small?!? They list the same dimensions regardless of which size spool you choose.