Balloon Math Stuff

Deciding which one to use

We found that Kaymont is a good balloon manufacturer to use and their 1500 Sounding Balloon is around $60.
These guys inflated a 1500 to 10lbs lift and attached their 8lb payload to it, although Kaymont recommends using a much smaller payload. http://vpizza.org/~jmeehan/balloon/
It seems like the Sounding Balloons will probably make it through the Tropopause if they have a fast enough ascent rate, but for applications where the balloon needs to stay in the Tropopause for a long amount of time the Cold Weather balloons are probably better.
The math on their site as far as the weight ratios go is:
- Average Weight: The weight of the balloon itsself (uninflated)
- Gross Lift: The recommended amount of lift to inflate the balloon to (the negative weight of the helium in the balloon)
- Nozzle Lift: The Gross Lift minus the Average Weight of the balloon = The negative weight of the filled balloon
- Payload: The recommended payload weight
- Recommended Free Lift: The difference between the Nozzle Lift and the Payload weight. If the payload weight is increased, you should also increase the Gross Lift so you keep the Recommended Free Lift. With this Free Lift value you should achive the specified Rate of Ascent.
If we use a 3000, it will go up to 125k feet in around 2 hours and a typical parachute should provide a descent of about 3-5m/sec which would at most take around 2 hours for it to come back down.

http://vortex.plymouth.edu/atmosphere/layers.html - This just says that our lowest temperature will be around -63 degrees celsius and should be around -23 degrees celsius at 125k feet.
http://www.utarc.org/wiki/index.php/Amateur_Ballooning_Compendium - This has good math info and data on atmospheric temperature
http://en.wikipedia.org/wiki/Earth's_atmosphere - General info on the atmosphere

When checking on balloons from Kaymont, I'd check to see how much the 1200-3000 balloons are for both the Sounding and Cold Weather Balloons and see which is cheaper. If the Cold Weather ones aren't that much more expensive I would go with them because it would have less chance of having problems when going through the Tropopause. All of the 1200-3000 balloons will support the 1050 gram payload so if there is a big difference in price between them get the one that seems most cost effective.
Also check to see if their parachutes will support up to the payload we need.

This calculator is pretty cool, it'll display the air pressure and temperature for any altitude: http://bpesoft.com/s/wleizero/xhac/?M=p

Each 1200 balloon has a 'base volume' of 4 cubic meters. That's 105 cubic feet. We might be overfilling the balloons in order to to lift our payload.. so let's say on the high side we need to put in 150 cubic feet.
3ric picked up a 290 cubic feet (2400PSI) tank. It's about 160 to 175lbs.
This should almost fill two of our balloons.. or maybe three if we don't need to overfill.