As a bugsmasher pilot, I’d be most worried about 40k ft of fishing line wrapping itself around the spinny bits on the front. What’s the tensile strength on that stuff?

Doubt it’d cause an immediate issue, but doesn’t sound very fun to remove.

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firesteelrain a day ago | parent | next [-]

3-6 newtons or about 0.7-1.3 pounds-force

Also it’s not 40k ft of wire. Altitude is 40k ft

The wire is about 16 ft for one leg of the dipole. That is the taught part. The other just floats in mid air underneath the payload

The community is very small and doubtful the sky will be filled with them

The balloons follow the jetstream from where they are launched. I have seen them fly over the Artic Circle, for example

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timeinput a day ago | parent | next [-]

I think there was confusion about whether it was tethered / what the tensile strength of the tether was. Reads like it wasn't tethered.

How did you communicate with it? Amateur bands? LoRa?

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LeifCarrotson a day ago | parent | next [-]

These and other high-altitude balloons are almost never tethered nor recovered - they're not a kite, that would be completely impractical.

You're nearing the altitudes at which the tensile strength of even supermaterials like Dyneema fibers are unable to lift the weight of their own tail, much less hold up against the tension of the jet stream. You'd need some kind of reverse rocket equation pyramid, where the topmost thousand meters have to lift the entire line, and are therefore made from line 0.6mm in diameter, and the next thousand meters are made of a slightly thinner, slightly less strong, slightly lighter fiber (because they don't have to lift the top thousand meters of line), and so on for the next 50-100km, depending on how much sag you expect the line to have.

"Oops, the balloon popped, excuse me while I do an ultramarathon across town spooling up my thousand-dollar tether from everyone's backyards...please don't cut it or trip over it or drive over it..."

No, it merely trails a 5 meter length of wire that acts as an antenna. You can receive the signals from hundreds of amateur receivers set up across the globe, often receiving transmissions at very long ranges. When the balloon eventually falls, yes, it's litter, but it's only a couple grams - go to your local park and pick up some trash, you can atone for a lifetime of HAB hobby sins with a single black bag full of alcohol bottles, fast food wrappers, and cigarette buts.

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dylan604 a day ago | parent [-]

> almost never tethered

yet you can't say never, hence the question. balloons are launched for different purposes. if you're trying to keep a balloon on station to gather local data, it's gotta be tethered. maybe not typical of a 40k' altitude, but they definitely use tethered balloons.

	▲	firesteelrain 21 hours ago \| parent [-]
		You are right; but in this case the topic was picoballoons which are free floating

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firesteelrain a day ago | parent | prev [-]

Yes, it is not tethered to the ground. The balloon is at the top, then 36awg wire, then solar panels and raspberry pi, then wire hanging down for lower half of dipole

Both top and lower part of dipoles are soldered to Raspberry Pi

It uses WSPR. Some of them use APRS but it is less common

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rogerrogerr a day ago | parent | prev [-]

Got it. Really cool project.

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dylan604 a day ago | parent | prev [-]

if you're not familiar, 36AWG wire is thin. very thin. according to [0], it is 0.1270mm. seems to me that it might melt free from friction thin.

[0] https://size-charts.com/topics/house-size-chart/wire-size-ch...

	▲	rogerrogerr a day ago \| parent [-]
		I’m familiar; I thought this was tethered to the ground. But it’s self contained within a few meters at 40k ft - not a problem. I do suspect if you encountered small gauge fishing line being used as a tether, you’d find at least some of it wrapped tightly around your spinner on the ground. Probably not much friction at play.