If you want to launch a pico balloon and circumnavigate around the world, following tips & tricks will be useful :)
Required Tools & Materials
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A tracker. We recommend LightTracker :)
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A lightweight solar panel https://www.digikey.com/en/products/detail/powerfilm-inc/MPT4-8-75/9559471
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Super capacitors. Optimum capacity for super caps is 3V 3.3F. Get two and connect them in series. https://www.mouser.com/ProductDetail/AVX/SCCR20E335PRB?qs=sGAEpiMZZMuDCPMZUZ%252BYl6pWnZvuEsiE2gaRVMyJvFA%3D
- 36 inch Clear Party Balloons. They are very cheap, durable and clear so radiation friendly, does not absorb too much heat. Also easy to attach (weld) balloons and seal filling tube with a heat sealer. But maximum altitude is about 10.000 meters. https://www.aliexpress.com/item/32699218436.html
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SBS-13. If you are looking for a professional envelope for higher altitudes (up to 14.000 meters) than check out Scientific Balloons Solutions products.
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A Heat Sealer. For welding balloons to each other and seal the filling tubes. https://www.amazon.com/Flexzion-200mm-Impulse-Sealer-Replacement/dp/B011TS3UWQ
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A Large Bulldog Binder Paper Clips. To temporarily seal the tube before heat sealing. https://www.amazon.com/Coideal-Bulldog-Binder-Drawings-Kitchen/dp/B07DGWY474
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Helium. Do not use hydrogen, helium is expensive but more safe because it's not flammable.
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Fishing Line.
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Very thin & light wire. For antennas and connections.
How to Fill The Balloons
Payload Weight & Free Lift
Before filling the balloons, you should decide how much helium you need to put in the balloons. After soldering completed, everything attached (panels, capacitors, wire antenna, fishing line, etc.) then measure the weight of the payload.
Let's assume it's 10 grams. So two of your balloons together should lift at least 15 grams to overcome the downward force of gravity. Under normal circumstances 15 - 10 = 5 grams free lift is enough for a safe ascending.
But 5 grams free lift is risky if your launch side is surrounded by high trees, buildings or power lines especially there is a strong side wind. So 10 gram free lift is more better and safer. This means your balloons should lift 20 grams total. If you use 2 balloons, every balloon should lift 20 / 2 = 10 grams each.
Fill the Balloons
Based on previous calculation, we start to fill a balloon until it lifts 10 grams. To do so, we are going to use a large paper clip (at least 15 grams) to temporarily seal the filling tube of the balloon as follows:
Start to fill the balloon with helium (but not too much), seal with paper clip, than measure the lift, than fill again, than measure the lift and repeat this until you get the target lift.
In this example my paper clip weighs 15.52 grams, so I fill the balloon until scale displays (15.52-10=) 5.52 grams.
Seal & Connect Balloons
After you fill the each balloons to lift 10 grams, seal the tubes permanently using heat sealer. Then trim the lower balloon's top and put it in the neck of the balloon as follows:
If the tab does not fit well into the neck, trim it until it fits without folding. When it's ok, then seal them to connect two balloons to each other as follows:
Solar Panel and Super Caps Connections
Final payload ready to launch:
