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Could World View balloons host a scale elevator prototype?

Posted by: Optimistic Brian - Sat Jul 26, 2014 7:28 pm
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Could World View balloons host a scale elevator prototype? 
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Post Could World View balloons host a scale elevator prototype?   Posted on: Sat Jul 26, 2014 7:28 pm
I've been impressed with the vision and test flight imagery of World View - a new space tourism company that plans to offer black-sky stratospheric flights in a pressurized balloon gondola. Their concept is so staggeringly obvious one has to wonder why such a business doesn't already exist.

But aside from the brilliance of their core vision, it struck me that their most important significance may be not at all obvious. I ask the following questions:

1. Could an evolution of their system ultimately host a permanent black-sky station that's tethered in place?

2. If so, could such a tether be utilized to transport passengers and supplies up and down to the station?

3. If so...you have a space elevator prototype!

In fact, although you might quibble with the exact altitude definition of "space," from a human perspective (i.e., black-sky = space) you might say that you have just created an actual space elevator - albeit one that contributes virtually nothing to orbital or escape velocities.

We know that tether materials and manufacturing processes are not yet equal to a full-scale, bona fide orbital-momentum-carried space elevator 30,000 kilometers long. But could they handle 30 kilometers? Or at least within practical sight of being able to handle that? And can a practical balloon system be made that could carry the weight of the tether and transit system in addition to a station?

The density of carbon nanotubes is 2.2 g/cm^3 (figure from Google search - I have no clue if it's accurate), so a 30 km-long tether made of that material with cross-section equivalent to 1 cm x 1 cm weighs 6,600 kg. The cross-sectional area could probably be a lot smaller than 1 cm^2 with a thin strip tether, so 6,600 kg is a maximum for the tether weight.

The Red Bull Stratos capsule weighed 1,360 kg, so this isn't an outrageous weight for a balloon system to carry.

If you can have a permanent, manned stratospheric station crewed and supplied by a tether elevator...then you could fly more than one with its own balloons and connect it to the first one. And another, and another.

Taken to an extreme, you've got yourself an entire resort / research campus with a black sky, where the pressurization aspects of space colonization technology can be explored routinely in full-g, just a few hours' vertical ride from the New Mexico desert. You've also got a regularly-operating space elevator prototype to learn about long-distance ribbon dynamics and safety issues.

Think about it as you watch this World View test flight:




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Post Re: Could World View balloons host a scale elevator prototype?   Posted on: Sun Jul 27, 2014 5:58 pm
Hi,

It is a nice idea, but when you do the math, it does not compute. NASA already researched this as well as other agencies and the result was not practical or sustainable. Which means you can pretty much do anything but will it be practical and maintainable.....answer no.

But, having said this balloon or floating stations, trips, tours, etc., this is going to happen!

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Post Re: Could World View balloons host a scale elevator prototype?   Posted on: Sun Jul 27, 2014 8:42 pm
VolksRocket wrote:
Hi,

It is a nice idea, but when you do the math, it does not compute. NASA already researched this as well as other agencies and the result was not practical or sustainable. Which means you can pretty much do anything but will it be practical and maintainable.....answer no.

But, having said this balloon or floating stations, trips, tours, etc., this is going to happen!


Can you be a little more specific than just "NASA hasn't done it, ergo it can't be done"?


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Post Re: Could World View balloons host a scale elevator prototype?   Posted on: Mon Jul 28, 2014 1:26 am
Actually NASA still sponsors the "space elevator challenge" so they don't totally discredit the concept. A full space elevator is rather beyond our means and technical ability though, and NASA knows this.

Using LTA craft to float a "tower" isn't really that far fetched. At its most basic, you could have a tube filled with hydrogen or helium to make it self supporting that theoretically should get you to 30 km or so. Lots of detail technical problems to solve though, and it wouldn't be cheap, 30 kms of high tensil material and many more cubic kms of gas add up.


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Post Re: Could World View balloons host a scale elevator prototype?   Posted on: Mon Jul 28, 2014 1:53 am
JamesG wrote:
Actually NASA still sponsors the "space elevator challenge" so they don't totally discredit the concept. A full space elevator is rather beyond our means and technical ability though, and NASA knows this.

Using LTA craft to float a "tower" isn't really that far fetched. At its most basic, you could have a tube filled with hydrogen or helium to make it self supporting that theoretically should get you to 30 km or so. Lots of detail technical problems to solve though, and it wouldn't be cheap, 30 kms of high tensil material and many more cubic kms of gas add up.


It appears the elevator-related challenges ended. Apparently Congress, in its infinite Creationist-led wisdom, doesn't consider such technologies worthwhile.

As to a hollow tube, you could probably do that by wrapping around a graphene sheet. Maybe you could wrap it such as to create a robust helium trap with extraordinarily low leakage rate.


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Post Re: Could World View balloons host a scale elevator prototype?   Posted on: Mon Jul 28, 2014 12:05 pm
Optimistic Brian wrote:
It appears the elevator-related challenges ended. Apparently Congress, in its infinite Creationist-led wisdom, doesn't consider such technologies worthwhile.


Or... being beyond broke, has to draw the line somewhere, like over the horizon technologies.

I think it went private or some university hosts it and NASA still endorses it.
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As to a hollow tube, you could probably do that by wrapping around a graphene sheet. Maybe you could wrap it such as to create a robust helium trap with extraordinarily low leakage rate.


Probably not necessary, the sheer and tension forces are distributed across the entire surface and you can keep pumping lift gas in from the ground. Plain mylar would probably be good enough.


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Post Re: Could World View balloons host a scale elevator prototype?   Posted on: Mon Jul 28, 2014 6:37 pm
With a vertical tube, the vertical surfaces would not be able to provide any buoyant support. Only surfaces with a horizontal component enclosing the lifting gas can provide lift. That means when the tube is perfectly vertical the entire weight of the tube would be hanging from the “dome” capping the tube. In this case, the tube material would need to have sufficient tensile strength to support its own weight over its entire length, just like a cable. If the tube weighs more than a cable, then a cable supported by a conventional balloon would be a more efficient design. Pumping lifting gas in from ground level, however, to compensate for losses would still be possible if the cable had a hollow core or at least a feed tube attached to it.


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Post Re: Could World View balloons host a scale elevator prototype?   Posted on: Mon Jul 28, 2014 6:48 pm
Not quite. Read what you wrote and think about it for a while. Consider boundary layer stiction and turgidity pressure. Also "dead weight".


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Post Re: Could World View balloons host a scale elevator prototype?   Posted on: Wed Jul 30, 2014 5:44 pm
A horizontal force can not cancel a vertical force. Internal hydrostatic pressure can act only horizontally on an upright cylindrical wall and will have no buoyant effect whatsoever against the vertical force of gravity acting on that wall.

Increasing pressure to the point where the tube becomes rigid doesn’t change that.

Only a force with a vertical element can hold the tube up in opposition to the vertical force of gravity. In this case, that force is the sum of the vertical elements of the vectors of hydrostatic pressure, which are always normal to the surface of the envelope. Only those areas of the surface with horizontal components can be subject to normal vectors with vertical elements.

But an open vertical cylinder has no horizontal surfaces. Only the domed surface capping the top of the tube has horizontal components, so only the domed surface can be subject to a vertical force due to hydrostatic pressure, no matter what that pressure might be. Therefore only pressure acting on the domed surface can oppose the weight of the tube.

Increasing the internal pressure to produce rigidity increases the upward force acting on the domed surface which also increases the vertical tension on the tube, far beyond the tension already created by its own weight, thereby requiring the material of the rigid tube to be that much stronger (and therefore heavier) than a merely buoyant envelope of the same dimensions.

A cable suspended from a balloon is clearly simpler and much more realistic. Ground-based compensation for the inevitable loss of lifting gas is still a good idea though.


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