High Altitude Balloon Internal Pressure Calculation?

[Darryl HEdges]

One of my hobbies is launching high altitude weather balloons carrying video cameras and scientific instruments to record various environmental parameters at high altitude — 90,000 to 100,000-feet.

I'm planning another project and I was wondering how much pressure is being exerted inside my balloons when they get close to their burst altitude of 90,000 or 100,000-feet? The balloons use helium as the lifting gas. The amount of helium placed in a 1500-gram (the weight of the balloon itself) balloon at launch is about 270 cubic feet. The balloon's diameter when it reaches burst altitude is about 30-feet. The balloon's volume at burst, according to the HAB-HUB Burst Calculator, is about 7.59 meters cubed.

I'm wondering how much force is being produced by the gas as it pushes against the opening at the base of the neck of the balloon. I'm looking to design and build a helium release mechanism to vent the balloon at altitude to slow its ascent to lengthen the amount of time that the balloon stays at close to its maximum altitude, then vent it again to start a slow descent.

Any thoughts?

 

[Baluncore]

Welcome to PF.

It will depend partly on the elasticity and burst pressure of the balloon. The internal gas pressure needs to be slightly greater than atmospheric pressure because the mass of the fabric and payload are being lifted by the balloon envelope which requires some initial shape and volume.

Once an altitude is reached where the balloon is filled due to gas expansion, there is no advantage in having a pressure greater than needed to keep the balloon shape. Gas at a higher pressure than needed will reduce the available lift because the gas density will be higher than necessary. That is a problem with burst pressure. It might be better to rip the canopy than burst it. Less gas and pressure would be needed.