Where the heck do you get a balloon?

Balloon
Engineer Fred Bruenjes prepares to launch a high altitude balloon last October.

As we countdown the final days until launch, some of our blog followers may be wondering where the heck you get a balloon big enough to lift 6 pounds of equipment 100,000 feet?  Here’s some background information about the weather balloons used by “Ascent” and the growing number of public projects that launch cameras to near space.

The are many companies on the internet where weather balloons can be purchased.  We have purchased 2 (one as a spare) from Scientific Sales, Inc.  Here is a link to their website with a variety of balloons in assorted sizes:

http://www.scientificsales.com/Meteorological-Balloons-Weather-Balloons-Sounding-Balloon-s/25.htm

Another popular vendor is the manufacturer Kaymont:

http://kaymontballoons.com/Near_Space_Photography.html

When deciding on a balloon to use, you have to first determine the amount of weight to be lifted along with the desired altitude you wish to reach.  The more weight you need to lift, the larger the balloon needed to hold the extra helium.  As a balloon rises in the atmosphere, it begins to expand as the outside air pressure decreases.  The balloon continues to expand until it reaches its maximum diameter at which point it bursts, allowing the payload to return to the ground by parachute.  Herein lies the problem: Several sizes of balloon can lift the same payload.  Choose a balloon that is too small and it will reach burst diameter before the desired altitude.  Choose a balloon that is too big and the balloon may burst much later than anticipated, causing the payload to return to the ground much further from the launch site.  Worse yet, the balloon may not burst at all and the payload could float above the ground for weeks.  Also, the larger the balloon, the more expensive it is and more helium required to lift the balloon’s own empty weight.

We have determined that we will be using one of Scientific Sales’s 1500 gram sounding balloons.  A sounding balloon, like a sounding rocket, is designed to carry payloads to suborbital heights for scientific measurements.  The designation “1500 grams” refers to the weight of the balloon before filling with helium.  Inflated with helium, it will span approximately 7 feet at launch and, at maximum altitude, should expand to approximately 27 feet across.  We estimate that we’ll use approximately 200 cubic feet of helium.

We should also add a note about the helium being used.  The helium sold in most party stores is a mixture of helium and compressed air.  This makes the gas cheaper to purchase and lets you inhale it for the high-pitch voice.  It also reduces the gas’s lifting capability.  For weather balloons and high altitude flights like ours, we will be using 100% pure helium.

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