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Thread: Lifespan of a weather balloon

  1. #1

    Default Lifespan of a weather balloon

    I am interested in building a cross-band repeater deployed on a tethered weather balloon for emergency situations where local repeaters may be overwhelmed or non-functioning due to power loss. I plan to install the whole setup in the back of a pickup truck with the tether on a large motor-driven spool. I want to be able to deploy it in a moments notice. My question is this: Does anyone here know, assuming it is never in the air for more than a few hours per deployment, how many times the balloon will be reusable? Do they wear out fast or will I be able to reel it back in and use it a hundred times? 75 bucks is a lot of money if I will wear it out the first few times I test it. All attempts to find this answer online show results pertaining to how long balloons hold their gas ~ which I am not concerned with. I need to know how many times they can be reliably filled up before wearing out and tearing.

    Thanks!

  2. #2
    Super Moderator 5B4AJB's Avatar
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    They usually burst at high altitude due to extreme internal gas pressure, I think they are permeable, so the gas will eventually leak out and not have enough lift.

    Mylar balloons are not gas permeable and stay up indefinitely, they are also a better radar target.

    Maybe a couple of survival blankets heat welded together would give you enough lift?

  3. #3

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    I don't plan to let it go much higher than a mile or two and would account for expansion. As for gas retention, I do not intend to have it deployed for any more than a few hours at a time, so whether it will stay inflated or not isn't an issue. My singular concern is how many times it can undergo the inflation and deflation process while retaining its integrity. In other words, can I deploy it on 100 different occasions reeling it back in between or will the material fail due to the repeated stretching?

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    Super Moderator 5B4AJB's Avatar
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    Personally, I would go with metallised Mylar, it's far cheaper and filling it with a mixture of hydrogen and oxygen produced by electrolysis of water from solar power is as free as it gets.

    You might not want to make this bigger than about 4 space blankets though as the resulting static it will pick up will likely cause self-ignition and may be quite loud at ground level.

    Sounds like fun.

    Helium is a rare, finite resource and I can't stand the thought of it being used up, even for science...

  5. #5

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    Mylar doesn't stretch, id have to send it up partially empty. I think I'll stick with a normal balloon.

    Air has a density of 0.001225g/cm^3
    a 2:1 mixture of hydrogen and oxygen obtained from electrolysis has a density of 0.00044g/cm^3
    Hydrogen gas alone has a density of 0.0000899g/cm^3

    I think i would be sacrificing a heck of a lot of buoyancy going with that 2H₂ + O₂ mixture, so i'll do the math. I intended to use the less dangerous pure H₂ and just get a compressed tank from the welding supply. But lets say for fun we make it with chemistry and not electrolysis...

    Two baofengs come in at 1 pound. with balloon, nozzle, diplexer and antenna, I anticipate the need for 3lb of buoyancy. Lets call it a 1,500g payload. Air minus Hydrogen = 0.001135g/cm^3 displacement. That's 1,322L of hydrogen, and at STP, 59mol of H₂.

    To make 59mol of H₂ using KOH, water and aluminum, I need 39.4mol of potassium hydroxide. That's 4.87 pounds KOH (or 3.391 pounds NaOH) to make that much gas. The average party balloon takes about 1 psi over atmospheric to inflate, so I will expect to multiply those numbers by 1.14 to be on the safe side. You know what..... that's just too expensive. Yea, scratch that.

    Lets say I did run a dry cell and make a 2:1 H₂ O₂ mixture. At .785g/L lift, I need 1910.9L of that gas. That's 7.4 foot diameter. I started off with the intention to discredit the idea of using mixed electrolysis gas as that seemed too heavy at first thought, but I must admit, I now agree with you!

    5B4AJB, thank you for that idea! You are 100% correct! Way cheaper, easier and still of manageable balloon size.

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