Half a croissant, on a plate, with a sign in front of it saying '50c'
h a l f b a k e r y
Recalculations place it at 0.4999.

idea: add, search, annotate, link, view, overview, recent, by name, random

meta: news, help, about, links, report a problem

account: browse anonymously, or get an account and write.



Vacuum Balloon Sun Shield

Millions of floating reflectors balance global warming
  (+2, -1)
(+2, -1)
  [vote for,

I just read an article indicating that "GeoEngineering", modifying the Earth's environment on a global scale, is now entering mainstream thought as Something We Might Need To Do (see link). The problem is global warming, and the time-frame for putting a solution in place appears to be shrinking faster than originally calculated. Remember that while rainfall patterns will change with global warming, that is not as big a threat to civilization as the icecaps melting would be, causing the oceans to rise 60 meters and drown seaside cities all over the world. Modern civilization should therefore consider preventing that to be something of a priority.

In the longest term the best solution is to get all those millions of tons of carbon dioxide gas out of the atmosphere, because putting it there is the root of the problem. This is so much more easily said than done, though, that no method of doing it can be implemented quickly enough, before it is too late.

In the medium term the best solution is probably to put some sort of shade in place in Space, between the Sun and the Earth, to block a small percentage of impinging sunlight. But we don't have the tech to do that as quickly as we need to do SOMETHING. We are thus stuck with doing something in the Earthly environment on a large scale -- "geoengineering", that is.

When possible, "large scale" should mean "mass production", which can involve many of the tools that our modern civilization has available. And it is perhaps fitting that the same productivity that has led to this problem might be employed to solve it. We just need a solution that doesn't destroy any ecosystems, and can last a long time. An example of something that probably won't work well is to build a forest of mirrors north of the "tree line". Often snow-covered, that darkish landscape is now exposed and absorbing sunlight; mirrors could prevent that and thus keep down the temperatures there. But for it to not get any sun, by being shaded all year long, means what little ecosystem it has will be destroyed, Not A Good Thing. Also, there is no equivalent amount of stable landscape near the South Pole, on which to mount an equivalent number of mirrors, to protect that region. And dust in the air would gradually reduce the effectiveness of the mirrors, anyway, unless they were cleaned often. We need a better approach!

In this Idea, "better" involves putting the system in place and then mostly forgetting about it. It can fall into the "out of sight, out of mind" category. It should not significantly interfere with the day-to-day activities of any life-form.

As you may already know, a "vacuum balloon" is a simple solid spherical hollow shell that has no air inside it at all. If the weight of the shell is less than the weight of an equal-volume amount of air, it will be bouyed upward, exactly like submarine is buoyed upward when it reduces its weight-to-volume ratio by replacing water in its ballast tanks with air. The main problem that vacuum balloons have is, ordinary air pressure causes them to be crushed. But who says we have to make them where the air pressure is ordinary?

Let us do our construction of vacuum balloons in two stages. At ground level a factory can make them almost complete, hollow spheres with one small hole each. We then transport them to high altitude, evacuate them, seal them, and release them. Now the shells only have to resist the much lower air pressure of the high altitude.

Let us assume here that by dealing with the air-pressure problem in that way, we can make these shells out of some ordinary lightweight metal like aluminum. Highly reflective, a mirror in any direction, each one we can make float at high altitude would reflect some sunlight away from the Earth. Impermeable to atmospheric gases, they could float/aloft for many years. ENOUGH of them can successfully combat global warming!

It is important to pick an altitude that is higher than most clouds. We should prefer an altitude that is even higher than most jets fly, just to prevent collisions --although the jets would probably not be damaged; they are built to survive impacts with much-more-solid birds. No, we want to prevent collisions so they stay aloft longer!

A possible difficulty here involves the "place" at which we do the necessary work at high altitude, evacuating and sealing the balloons. Mount Everest might qualify, but we don't want to release all our vacuum balloons at that latitude. We would prefer that most of them, in fact, be released near the Poles, to reduce the sunlight that is melting the icecaps. Atmospheric wind-circulation patterns might even keep most of them over the poles, too.

What we cannot do is release them while flying a jet at a thousand kilometers per hour; they are too fragile for that. We need a relatively stationary high-altitude platform, to which we can easily transport the prepared but non-evacuated shells. A tethered aerostat might qualify (with additional balloons holding up the tether, which is used as a conveyor to transport the shells). No aerostat yet exists that is large enough to be a factory such as we need, but that is much more due to a lack of money than a lack of technology. As the urgency of the need to solve the global warming problem becomes more apparent, the money should become avaliable for solutions, perhaps including this one.

Vernon, Oct 22 2008

GeoEngineering article http://www.sciam.co...ol-earth&print=true
As mentioned in the main text [Vernon, Oct 22 2008]

About aerostats http://en.wikipedia.org/wiki/Aerostat
All sorts of balloons and blimps and dirigibles qualify. [Vernon, Oct 22 2008]

Please, not mylar http://www.nytimes....all/20bills.html?em
[normzone, Oct 22 2008]

Lighter than air http://en.wikipedia...ki/Lighter_than_air
Wikipedia article mentioned in an annotation [Vernon, Oct 23 2008]

Balloon Notions Balloon_20Notions
A HalfBakery posting with certain relevant calculations. [Vernon, Oct 23 2008]

Atmospheric Pressure http://en.wikipedia...tmospheric_pressure
Another relevant Wikipedia article [Vernon, Oct 23 2008]

Lead Balloon http://www.youtube....watch?v=HZSkM-QEeUg
It actually flies! [Canuck, Oct 23 2008]

More on Vacuum Balloons Aerogel_20Vacuum_20Balloons
Unobtanium exists for vacuum balloons! So, make these by the million, give them a nice reflective coating, and let them float for years, protecting against Global Warming. [Vernon, Oct 24 2008]


       Interesting, [Vernon].   

       Your basic premise is probably okay - I'm really not sure how much reflectance needs to be added to the earth's surface to help with "global warming". <that's a good question - are we still predicting global warming? Isn't it global cooling now? Or are we still using the catch-all "Climate change" because we really don't kow what, if anything is going to happen? Any bidders? Informed bidders that is?>   

       The problem is with vacuum baloons. Vacuum baloons are an interesting force balance - but one that doesn't stand a chance in high altitudes. The advantage to a helium or huydrogen baloon is that the baloon walls essentially don't have to support very much force - the baloon expands as the pressure drops at high altitude - it's a self regulating system in that the ballast gas expands to match the pressure outside. With your vacuum baloon, there will be no subsequent expansion. I think you'll find that the wall thickness required <or should I perhaps say the wall thinness> for high altitude will be unfeasibly thin. In fact, I bet there's a nonlinear relationship that makes vacuum baloons less efficient at greater altitudes, with optimised wall thickness. The engineering gets complicated, but essentially thin walled vessels are no good at withstanding compressive forces. With the exception of concrete, soils, etc, you'll find that most engineering materials are much better under tension, rather than compression (look up "thin wall buckling").   

       <Edit - to clarify - I'm not trying to say concrete & soils are good at tensile forces. What people don't realise, is that with a thin wall vessel under compression, it's not the compressive strength of the material that's important. It's the bending strength (yielding strength and stiffness) that are important, because things fail from buckling, when subjected to compressive forces. </edit>   

       Why not propose Mylar coated helium or hydrogen baloons, do some research into hydrogen-retaining membranes (are there any?) because hydrogen is 2X better than helium in lift.
Custardguts, Oct 22 2008

       Every time I see a plan that involves making sure our energy-starved world gets less free energy I gotta wonder what people are thinking.
FlyingToaster, Oct 22 2008

       I don't see any advantage in doing this whatsoever.   

       If you want to reflect light, put up a very big, thin mirror in geo stationary orbit. Using balloons at cloud height would be very expensive, and very inefficient since the light is travelling in and out of the atmosphere. Having spheres would mean only the top part of the object is reflecting the right way, the rest of the material is wasted. Also, the balloons wouldn't stay put, if you did manage to create vacuum balloons, they'd float all over the place and collide with each other, which would probably implode them.
mitxela, Oct 22 2008

       Please, not mylar. I enjoy watching one football game per week. (link)
normzone, Oct 22 2008

       [Custardguts], read the first link. The recent evidence really is for an unexpected increase in the rate of icecap melting. Next, for a vacuum balloon, the important thing is the mass-to-volume ratio. If I take a sphere of a certain size and double its dimensions, except for the thickness of its walls, then its mass will have gone up 4 times but its volume will have increased by 8 times. The only question is, how thick does the wall need to be to withstand air pressure at a specified altitude? Also, the sphere-shape is generally pretty good at resisting compression, when the compressive force is applied evenly from all directions, which is the situation for a vacuum balloon. There is no doubt that thin-wall vacuum balloons can work at high altitude; their biggest problem has been keeping them from being crushed at low altitude. And remember, mylar LEAKS. Solid metal generally doesn't. Your mylar balloons will last for a few days each, and constantly have to be replaced. If you are trying to keep millions and millions of them aloft for many years, you have a major problem!   

       [FlyingToaster], incident sunlight worldwide only needs to be reduced by 1 or 2 percent. If we can concentrate that reduction at the polar regions, where we want ice to re-freeze and accumulate, then solar power plants (none planned for the poles) will all work just fine and unaffectedly.   

       [mitxela], you didn't read the main text here very well. I specifically stated we don't have the tech yet to put up big mirrors in Space fast enough. Also, you are wildly mistaken about balloon collisions. Most of the time they will all be travelling together at the same speed, carried by wind. How often do hot-air balloons in a race collide, when not changing altitude? I can agree that some extra strength will be warranted because SOME collisions will happen, but most such will be quite gentle, due to the balloons mostly moving together in the wind stream.
Vernon, Oct 22 2008

       How about very low pressure hydrogen glass balloons? I remember an add for a forever balloon that was blown glass filled with H2 with a little string and a base so it could be used as a desk accessory. So blow very thin large glass spheres in a low pressure H2 environment and then put Al on the outside of the heavier half for a cool mirror effect
MisterQED, Oct 23 2008

       //There is no doubt that thin-wall vacuum balloons can work at high altitude//   

       Righto, unless I read otherwise, I call bullshit.   

       //If I take a sphere of a certain size and double its dimensions, except for the thickness of its walls, then its mass will have gone up 4 times but its volume will have increased by 8 times//   

       That's nice, but your walls will buckle horribly. Yes, spheres with thick walls are the ideal shape for compression, but thin walls just don't cut the mustard. Look up the wiki link for vacuum baloons - I like how they link to the unobtanium page.   

       At an altitude of 10,000m, air density is down to roughly 1/3 of sea level - so your vacuum baloon is generating 1/3 the lift. That gives you 400g of aluminium per cubic metre of baloon for neutral density. So for a 1 cubic metre baloon, you've got a radius of ~.6m, and a surface area of 4.8 square metres. So you get 0.03mm wall thickness to hold back 33Kpa outside overpressure. You're dreaming. Just for Yuks, a 10 cubic metre baloon gets a wall thickness of 0.066mm. You're still dreaming.
Custardguts, Oct 23 2008

       Instead of reflecting the sunlight it with mirrors, use photocells and produce electricity from it. Cover every flat surface with photocells and convert the sunlight to electrical energy. Funnel the electricity into the electric lines to run the meter backwards or store it in rechargeable batteries.   

       This requires no new technology and with greater use will make photocells cheaper to make and inspire improvements to make them more efficient.   

       This reduces the energy warming the earth and reduces the use of fossil fuels to make electricity, thus killing two ecological disasters with one implementation.
theGem, Oct 23 2008

       [Custardguts], some of your figures are wrong. I had once read somewhere that a very large vacuum balloon was feasible, at very high altitude (rather higher than 10000 meters). Now I'm trying to get data together to do the math, to see for myself. Certainly the aluminum-foil-thin walls you talked about won't work. I'll be editing and adding to this message when I'm done figuring.   

Well, I'm not done figuring yet (and don't have them with me at the moment, sorry), but my preliminary figures indicate that a sphere of air at sea level, 100 meters in diameter, has a weight of well over 600 metric tons. If a shell that size weighs less than 20 kg per square meter, then the evacuated sphere should lift. I would have to drop any notion of using aluminum for a sphere this size, but perhaps some carbon-composite honeycomb structure with a thin skin would be strong enough to resist air pressure. A sphere that is a kilometer in diameter would allow us to play with 1000 times as much weight, and only 100 times the surface area to construct; it means we get to play with about 200kg per square meter of shell-material. We would want to use significantly less than that, if the balloon is to fly at high altitude, of course.

       Unfortunately, even if I haven't made an error and such a vacuum balloon is feasible, it is too big to think about mass-producing millions of them for this Idea. Another notion is needed to make it work as described here....
Vernon, Oct 23 2008

       Perhaps we should submit this idea to Mythbusters to get Adam & Jamie to build it for a future episode. Don't laugh, these guys managed to make a lead balloon that floated! (link)
Canuck, Oct 23 2008

       Of course if you fill something with hydrogen it will all leak out leaving you with a vacuum balloon anyways.
FlyingToaster, Oct 23 2008

       Feel free to point out where my figures are wrong. I'm just as fallible as the next guy.   

       Problem with going to higher altitude is, you get less buoyancy to play with. So as you go up, your available wall thickness is just going to get thinner and thinner. I get, for a 1000 cubic metre baloon, at 10kPa (1/10 sea level) an available wall thickness of 0.092mm. The numbers are working against you.   

       The design of a baloon (thin flexible membrane under tension) is much more inherently stable than this vacuum baloon (thin rigid wall under compression). The reason for this is thin wall buckling.
Custardguts, Oct 23 2008

       [Custardguts], the advantage to higher altitude is that there is less pressure for the shell to resist, allowing it to be thinner. Your figures are not wrong by a lot, but--- (for example, air pressure is about 1/3 of sea-level at about 8000 meters, not 10,000 meters). I'm not sure where you got your weight-of-air figure; I linked my "Balloon Notions" Idea because it shows a way to compute the mass (not weight) of a volume of air at STP. In some respects mass is more important than weight, in these calculations.   

       Last night I realized that with respsect to vacuum balloons, "unobtanium" actually exists. It was discovered decades ago, and research into it is ongoing, but so far as I know, nobody thought of this particular application for it before. I'm going to post a separate Idea here about that, and then link this Idea to it.
Vernon, Oct 24 2008


back: main index

business  computer  culture  fashion  food  halfbakery  home  other  product  public  science  sport  vehicle