Now, launching a weather balloon sounds straight forward enough, blow up, attach payload, release! But this isn’t a party balloon we’re talking about, no, for a weather balloon, whether its a meteorological balloon or camera balloon, there are a few things you’ll need to consider when planning your launch:
Size Does Matter
Don’t be tempted to buy a smaller balloon and just pump in more helium! Your balloon is going up up up, to around 90’000 feet off the ground. At high altitude balloons expand due to the pressure outside decreasing while the pressure inside remains the same. As your balloon rises through the atmosphere it will expand as the air thins. A weather balloon 5 ft wide at launch will reach a width of about 20 ft at peak altitude. It needs the extra inflation room for this. Your balloon will eventually pop, hopefully at its maximum altitude. Its not gonna reach this if you over fill it. So get the right sized balloon to take the weight of your radiosonde or weather balloon camera – of course if your balloons maximum altitude is far above what you need it for you have some wiggle room & can experiment with inflation, but at your own risk!
Each cubic ft of helium will lift 28g of weight, however, the radiosonde needs to be lighter than this for the weather balloon to rise. The balloon will rise faster the smaller the weight. The difference between the radiosonde weight and the liftable weight is called the ‘free lift’. You can calculate the balloons accent rate easily as it works out at 300ft per minute for every pound of ‘free weight’. The faster your balloon ascends the less chance of something going wrong – a blow out, equipment batteries failing, the payload landing further down wind and being harder to recover.
Now a weather balloon is not gonna weigh much right? Stick it in your pocket almost (if you have really big pockets). But a helium canister does! It’s a large heavy steel tank and a 125 cubic ft helium canister will stand about 6 ft tall and weigh a hefty 100 pounds. So you’ll need a car or jeep for transportation, especially if you’re going to track your payload down when it lands.
There’s nothing more frustrating than losing your payload, especially if you couldn’t afford the equipment to stream the images/data directly back. If you’re relying on GPS tracking to recover your data manually you had better spare a thought for the poor electronics your hurling into the freezing environment of the upper stratosphere! At 90’000 ft up the temperature is about -50 degrees C and your average battery will cease to function. However you have a better chance of maintaining connection with your beloved balloon kits if you use lithium batteries NOT lithium ion batteries. No no, different kettle of fish. You can buy energiser lithium batteries and they last 8 times longer than standard ones but more importantly they can withstand the cold temperatures of the upper stratosphere!
The Actual Launch
Now, on the day you need to carefully consider launch area, and weather conditions: Don’t launch near a military installation! They might think they’re under attack, and while the idea of men in camouflage running around on red alert may sound funny to you, I bet the idea of them shooting down your weather balloon isn’t! Don’t interfere with military air space and they won’t interfere with you. Next you need to make sure your launch area is away from obstructions such as trees and telephone polls, preferably not in a built up area for retrieval purposes.
For obvious reasons no wind is preferable, but look up the wind direction before you launch so you know which direction it’ll land in. If your launching a camera balloon you’ll need a sunny day for decent exposure on your aerial photography.