Idea I can't do anything with - help yourself.

JunkMonkey

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I was reading a kids' science magazine that we subscribe to the other day and in an article about colonising Mars there was an item that caught my eye.

Dirigibles on Earth are filled with Helium because it is lighter than air and not explosive.

What is even lighter than Helium and would make a really buoyant balloon? A vacuum.

If you could fill a container with vacuum it should float. The problem is on Earth, because of the thickness of our atmosphere, the ratio of the weight of the structure required to resist collapse to the 'lift' it contained means it would never get off the ground.

Not so on Mars apparently. Atmospheric pressure even at ground level is so low that vacuum-filled balloons are feasible.

Which got me thinking - what if these structures were built in space (where vacuum is cheap) rather than on the surface. They could be used as 'parachutes' to lower probes / manned craft to the surface and then be used as flying rovers / transport ships or with a little boost returned to orbit as shuttles. The fuel savings would be huge.

Then I got to thinking if you could make them in space why not make them in Earth orbit? Ok they would have a lower limit before they collapsed but extremely high altitude balloons have their uses.

No idea what to do with this notion; so if you can use it, it's yours.
 
Reminds me of Buckminster Fuller's Cloud 9, a spherical city 800 meters (or larger) across. floating in the sky.

It sounds like science fiction, but here's how Fuller proposed a Cloud Nine would work. A half-mile (0.8-kilometer) diameter geodesic sphere would weigh only one-thousandth of the weight of the air inside of it. If the internal air were heated by either solar energy or even just the average human activity inside, it would only take a 1 degree Fahrenheit (0.56 degree C) shift over the external temperature to make the sphere float. Since the internal air would get denser when it cooled, Fuller imagined using polyethylene curtains to slow the rate that air entered the sphere. He wanted to build Cloud Nines and anchor them to mountains or let them drift so their inhabitants could see the world. One of the more practical uses he proposed for them was as disaster sites for emergencies.
 
Reminds me of the end of Seveneves where Stephenson talked about the "baskets" that would orbit earth. I'm paraphrasing from memory, but basically each basket was tethered to something in space/the upper atmosphere and it would travel the globe in a stable, predictable pattern. The tether was (IIRC) variable in length. This meant they could retract it to gain momentum, extend it to slow/stop and the tether basically never stoped rotating. There were landing pads where the basket landed, people/goods get on/off, and then it would continue on its journey, all without the use of consuming a fuel for propulsion.

Cool, concept -- but the post-climax falling action portions of a Stephenson book is typically pretty hit or miss. I like the idea of a vacuum balloon way more. That's super cool.
 
The problem is that floating in the upper atmosphere is 28,000 kmh slower than low earth orbit, so you have to have fuel weight or reentry shield weight. However, if the structure is tough enough it might slow down swiftly enough to not heat up in the process.

Building structures like this on earth wouldn't be a bad deal either - build it like origami and pull them open to produce a vacuum. No need for a pump.
 

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