Re : A High altitude balloon design idea

[Krishna Sagarreddy]

Hi all,

I would like to clarify something.I know that high altitude balloons work on the principle of low density of gas in the balloon and atmospheric buoyancy. However, their maximum ascent is limited by their inability to survive a steep rise in internal pressure vs low external pressure at a designated high altitude. However, I have a special balloon design (please see the attachment )which could survive the rise in internal pressure at high altitudes. My question is how high could it ascend? If I understand correctly, downward forces on the ground would be gravity and atmospheric pressure vs strong buoyant forces, whereas at a high altitude, the forces are mainly gravity vs kinetic enerygy gained by the balloon because of buoyant forces. 

I am also attaching my idea of testing this special balloon’s design in the near vacuum in a lab. Looking forward to your responses.

Many thanks, 

Kind regards,

Krishna

[Steve]

The first thing I would say is that lighter than air ballooning has been around for well over 200 years and if there was some simple scheme like this for increasing maximum altitude then it would have been discovered and be well known by now.  But all questions are valid.

The thing that mostly sets the maximum altitude a balloon can get is the size it can reach without bursting.  This will be mainly determined by the differential (inside to outside) pressure difference.  The altitude this occurs is set by the amount of gas fill at launch (and that dictated by the balloon weight + payload weigh and the desired ascent speed). 

There are other effects going on such as the temperature affecting the balloons properties, gravity decreasing slightly with altitude but these less important.  Issues such as entering float due to slow ascent rate have also been ignored.

All that would happen in your 2 balloon design is that as the 1st balloon would need more gas to lift the added weight of the 2nd balloon - at some pint before burst the 1st balloon it would start to transfer gas to the 2nd balloon until such time they were equal pressure.  At which point they would continue to ascend until one of the burst - which will be the same as if that balloon alone had been released with the amount of gas it contained at burst

    Steve

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[Krishna Sagarreddy]

Thank you very much for answering my question. I felt that this might be the case. However, My imagination has took me to into a very interesting and weird places. I have some ideas for advancing such balloon design.

1) The balloon design can be modified to a 3 or 'n' number of equal volume (Something like a coronavirus shape) interconnected balloons with valved connection and central one filled to brim but the others deflated but can be inflated to peak volume by rise in internal pressure. My belief is that with the advances made in vacuum chambers, such balloon can be stress tested at the ground level on whether they can survive near vacuum or not.

2) As far as temperature is concerned- using day and night cycle will be one solution to keep the gas either at extreme hot or cold temperature. Again this can be again stress tested in vacuum chamber under intense warm/cold environments.

3) As far as material design is concerned, material advances made in astronaut's suit sound quite promising.

At the end of the day, my main question is that if such a hypothetical balloon survives by some super-intelligent design - how high will it ascend? I think it would be ineresting to know whether it could reach LEO or not.

Regards,

Krishna

[Steve]

The highest balloon got to 53km - there is to reason better materials should not be able to get a balloon higher - but I doubt that even the lowest of Low Earth Orbit altitudes 250km? can ever be reached.

The atmospheric scale height of the earth is about 8.5Km - that means (very roughly) for every additional 8.5Km in height, the air density decreases by a factor of e (2.71828183...) - meaning to get 8.5km higher the balloon would have to encompass 2.71828183x the volume while retaining the same weight.  The volume of a balloon is proportional to the radius cubed while the surface area proportional to the radius squared (the weight of the balloon being related to the surface area and skin thickness) - so my rough calculation suggests that for every 8.5Km the material strength would have to increase by a factor of about 2. I.e. it would have to get thinner by a factor of 2 or lighter by a factor of 2 - while retaining the same tensile strength).

There are 23 x 8.5km between 53km and 250km - so good luck finding a material 2^23 (8,000,000x) stronger than the 53km balloon.

I admit this is all rough and ready calculation - and the upper atmosphere may not follow the scale height rule exactly - but it won't be hugely out.

    Steve

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[Krishna Sagarreddy]

Thanks for your meticulous reply. I clearly see what you mean but that is where I believe my gas redistribution concept comes into play. Instead of finding such strong material, I aim to redistribute the gas volume between the balloons ( simplest shape being a dumbbell balloon with an elastic membrane with pinhole at its centre located in the middle of the bridge) . Essentially when the 1st balloon is inflated to pressure 'P' the bridge is soft clamped to keep the 2nd balloon deflated and the valve unexposed to pressure.  When the clamp is released slowly, a small rise of pressure in the bridge keeps one half inflated while the other deflated, however adding more pressure will stretch the bridge and the membrane increasing the pinhole diameter leading to gas transfer. My trick is to use near vacuum to increase the internal pressure.  This should atleast keep the 1st balloon safe in theory till both balloons expand to max volume and there is no reason not to use a bigger deflated balloon(Asymmetric dumbbell).

I played with ping pong balls and drowning them in water is a profound experiment to me. Not because of denisty and buoyant forces, but because the ping pong ball stopping also indicates the end of water column. It would be amazing to see a High altitude balloon survive and suspend at the limit of the atmosphere. Interestingly, It has a good kinetic energy at 53 km(current record) and gravity's effect should only reduce from then- so will the intertia carry the survivor to 250 km? No idea. I want to test this concept. Kindly advice.

Regards,

Krishna