Using Aircraft & Balloons to Deliver 'Sunscreen' to Upper Atmosphere?

[Spinnor]

In the news we learn that aircraft (that don't exist) flying to 12 miles in altitude might be used to deliver "sunscreen" to the upper atmosphere. Could we use a carbon fiber fabric to make a strong, relatively lightweight, and flexible smokestack that might be supported by large helium lifting balloons which were tethered to the ground to get close to the 12 mile altitude needed and then use it to pump "sunscreen" into the upper atmosphere? At some point we may need to drop the average Earth surface temperature. Impossible, improbable, uneconomical? Thanks for your thoughts.

News stories, https://www.theguardian.com/environ...eering-could-be-remarkably-inexpensive-report

https://www.cnn.com/2018/11/23/health/sun-dimming-aerosols-global-warming-intl-scli/index.html

From, https://en.wikipedia.org/wiki/High-altitude_platform_station#/media/File:High_Altitude_Airship.JPG

 

[anorlunda]

All forms of geoengineering are highly speculative and controversial.

If this thread becomes too speculative, it will be closed. So please everyone, if you reply give citations and links.

 

[Spinnor]

All forms of geoengineering are highly speculative and controversial.

I would be happy if the geoengineering aspect were ignored.

How tall can a smokestack be built and could it pump tons of particulate into the stratosphere and at what cost per ton.

Or better maybe, what is likely the cheapest manor to get thousands of tons of particulate to the 20 mile mark.

 

[anorlunda]

How tall can a smokestack be built and could it pump tons of particulate into the stratosphere and at what cost per ton.

There is nothing in engineering experience that would allow an answer based on facts, or even existing estimates.that I know of.

 

[jrmichler]

There are a number of factors to consider.

1) The jet stream can reach speeds over 200 MPH, although at altitudes where the air is less dense. The total drag on a circular stack will be quite high. A streamlined stack cross section is possible, but would require a means to align it with the jet stream. Guy wires to hold it vertical are impractical, which leaves a really large balloon to pull it toward vertical.

2) A rough estimate is that a 10 foot diameter carbon fiber stack 0.02" wall thickness by 60,000 feet tall will weigh on the order of 300,000 lbs. Something has to hold it up.

I can keep going if anybody is interested.

 

[Spinnor]

The jet stream can reach speeds over 200 MPH

Winds are a bit calmer at the equator I would bet, but the wind drag would be huge.

 

[russ_watters]

Could we use a carbon fiber fabric to make a strong, relatively lightweight, and flexible smokestack that might be supported by large helium lifting balloons which were tethered to the ground to get close to the 12 mile altitude needed and then use it to pump "sunscreen" into the upper atmosphere? At some point we may need to drop the average Earth surface temperature. Impossible, improbable, uneconomical?

It's likely possible to use such a "structure", but whether it is economical/practical is a tough thing to speculate on. The biggest difficulty I can see would be the effect of wind.

 

[Spinnor]

but whether it is economical/practical is a tough thing to speculate on

If engineers were given the task to design a way to move tons of particulate to the stratosphere in the least costly manor they would brainstorm first and then pull out the back of an envelope to quickly eliminate ideas?

Liking my idea less. Thanks.

 

[jrmichler]

Don't give up until you have done those back of the envelope calculations. Find the best location, get some numbers for winds aloft at that location, then calculate actual air drag. Then make the stack have a stream lined cross section, assume a way to align it with the wind, and calculate the drag again.

Then estimate how much aerosol can be pumped to the upper atmosphere. If the stack is designed for constant velocity, then as a first approximation, the cross sectional area is inversely proportional to the air density:
Altitude Diameter
0 10 feet
15,000 12.6 feet
30,000 16.2
45,000 22.6
60,000 32.4

Again, simplify by pretending incompressible flow, ignoring temperature effects, and try two different rates of friction loss:
1) 1" w.c. friction loss per 100 feet of duct = 600" per 60,000 feet. Extrapolating the ASHRAE duct friction chart, that's 940,000 CFM at 12,000 ft/min. At 80% fan efficiency, that's 110,000 horsepower. Recalculating as compressible flow would make the duct larger toward the discharge end.
2) Try 0.1" w.c. friction loss per 100 feet of duct = 60" per 60,000 feet. Extrapolating the ASHRAE duct friction chart, that's 300,000 CFM at 3,800 ft/min. At 80% fan efficiency, that's "only" 3500 hp. Still compressible flow, but not as much as Case 1.

The next calculation is to estimate how much aerosol can be conveyed at these flow rates. After that, how many airplanes / dirigibles / rockets / vehicles would be needed to move the same amount of material.

Take the resulting numbers and keep them handy for the next time that somebody proposes some form of atmospheric engineering that involves placing material in the upper atmosphere.

 

[Spinnor]

Take the resulting numbers and keep them handy for the next time that somebody proposes some form of atmospheric engineering that involves placing material in the upper atmosphere.

Nice analysis, thank you!

 

[jrmichler]

The paper that triggered The Guardian article is here: http://iopscience.iop.org/article/10.1088/1748-9326/aae98d/meta. The authors specifically mention a tethered hose as "not sufficiently mature technology", because they are trying to show that climate change geoengineering is practical and cost effective with existing technology.

Climate change geoengineering has been proposed for several years now, and tethered hoses have been proposed before. The Environmental Research Letters paper is a good excuse to do some back of the envelope calculations on a concept that is orders of magnitude less speculative than, say, space elevators. Even if (especially if) those calculations show that the concept is worthless.

The paper proposes lifting 1.5 megatons/year of sulfur, which is burned at altitude to create 3.0 megatons/year of SO2. One or more tethered hoses would thus be expected to send 3 megatons/year of SO2 to an altitude of 60,000 feet.

Now for the calculation: 3,000,000 tons/year X 2,000 lbs/ton / 365 day/year / 1440 minutes/day = 11,400 lbs/minute of SO2. One tethered hose would move 300,000 cubic feet/minute, weighing 23,000 lbs/minute of air. Sulfur dioxide melts at -104 deg F, and boils at 14 deg F. It would enter the hose as a gas, and leave as a mist or fog. If the entire amount of SO2 was carried with one ten foot hose, each pound of air would be conveying 0.5 pound of SO2 gas or mist. Dilute phase pneumatic conveyor manufacturers claim they can convey up to 10 lbs of solid product (in fine particles) per pound of conveying air. They also claim minimum conveying velocity about 2000 ft/min, with desirable conveying velocity 3000 ft/min. It appears that one tethered hose is theoretically capable of conveying the desired 3 MTPY of SO2 to the upper atmosphere.

The increased mean gas density would increase the fan power required to 5,000 to 6,000 hp. Large power plant induced and forced draft fans are already made in this size range.

Calculations to do yet: Air drag, lift required, tensile strength.

 

[anorlunda]

The paper proposes lifting 1.5 megatons/year of sulfur, which is burned at altitude to create 3.0 megatons/year of SO2.

Great post. But after this sentence, the rest of the discussion talks about sending SO2, not sulfur up the pipe. In what form is the sulfur at ground level?

 

[Baluncore]

In the news we learn that aircraft (that don't exist) flying to 12 miles in altitude might be used to deliver "sunscreen" to the upper atmosphere.

I get my power from PV on the roof of my house. If anyone blocks my sunlight I will demand financial compensation.

If more sulfur was included in the fuel of high altitude aircraft, for use when cruising at 35k to 40k feet, would that not provide a sunscreen without the need for a fragile smokestack that would be laid flat, or torn apart by the high altitude winds.

 

[anorlunda]

get my power from PV on the roof of my house. If anyone blocks my sunlight I will demand financial compensation.

I once asked a lawyer if I could sue to force my neighbor to cut his trees (or to tear down his high-rise apartment building) so that I could have solal panels. The answer was, "No."

The problems with geoengineering include:

• Unknown side effects.
• Inability to reverse the change.
• If there are winners and losers, who compensates the losers?

 

[Spinnor]

I get my power from PV on the roof of my house. If anyone blocks my sunlight I will demand financial compensation.

The political challenge might be greater than the engineering one. Some countries might benefit from a warmer globe.

 

[Sherwood Botsford]

The idea behind SO2 is that it forms a haze that reflects some sunlight. However when Pinutubu blew up, it put a fair amount of SO2 into the upper atmosphere, and indeed it did cool the Earth for a year. It also resulted in lower precipitation. Dropping the temperature but creating drought isn't a win.

More discussion here: https://Earth'science.stackexchange...o-the-atmosphere-have-a-global-cooling-effect

 

[Jon Richfield]

FWIW I don't believe that this approach is right-headed; I do approve of the climate-engineering principle, but the chimney/pipe approach is bad engineering. There are better approaches, even if we ignore tickling up volcanoes.

One is to use the toroidal vortex approach. Build quite modest ground smoke-ring blowers (you also could have floating ocean-going versions). You would have to work out the engineering and no doubt do a bit of experimentation to tune the design, but in any case charge the chamber with say, a few tonnes a time of a suitable mix of H2S and a lighter gas such as H2 or CH4 plus O2. (I am uncertain about the O2; it might be better to rely on ambient air, but as much of the burning would have to be the higher up the better, I favour some O2). The mix should be buoyant, but not rely on buoyancy to gain altitude. Instead it should be prepared by explosive launching of the toroidal vortex. It could be ignited from the ground by laser. You could launch a new charge every few minutes I reckon.

A less imaginative approach would be to launch a similar mix, but with greater buoyancy, in polymer bags, probably self-combustible, or rapidly degrading at high altitude so as to be bio-friendly. Each bag to accommodate a few tonnes or so. Launch them in the evening and have them ignite themselves in the sunlight next day. Simple? Of course not; nothing is simple till you have worked out the bugs.

But it beats having to invent multi-km chimneys...

Let alone disposing of them afterwards.

As for the paper on why you can't use planes, that was embarrassingly naive. You certainly could use planes and some other measures efficiently, but I have said enough for now.

 

[Sherwood Botsford]

I've seen serious discussions of high altitude wind turbines for power generation. Right now the problem is the tether. A tether to 35,000 feet at a 30 degree angle is 70,000 feet -- 14 miles long. At present we don't have anything that can support it's own weight in 14 mile lengths.

 

[Baluncore]

At present we don't have anything that can support it's own weight in 14 mile lengths.

You are using paralogical analysis to dismiss the possibility of a tether. You are ignoring the fact that the tether material might be buoyant. An HDPE rope is buoyant in seawater and so can hang up to the surface from the bottom, without having to support it's own weight. A cylindrical tube that contained helium filled cells, or had external He balloons attached, could be buoyant in the atmosphere. So we do have structural materials that could make the tether today.

So why do we not do it? The magnificent solution costs most up-front, and is also most vulnerable to a single catastrophic and unrecoverable failure. Magnificent solutions are favoured by corporate enterprises that can control governments and want to dominate the energy production market. But they have missed the boat here, as distributed ground based wind and solar are now expanding at the rate they can be funded.

The idea that an altruistic consortium might build a magnificent smokestack to deliberately pollute the upper atmosphere is similarly fabulous. There are many lower cost management strategies that involve less risk to each and every one of our triple bottom lines.

There will always be driven people who get an idea stuck in their head, and who then pursue it for the rest of their lives through lobbying any organisation gullible enough to listen or provide a platform for publicity. Our aim should be to debunk the meme before it spreads like a virus to consume other peoples lives and resources.

 

[Sherwood Botsford]

I considered this, but rejected it for drag reasons. I figured a solid sided ( from wind point of view) cylinder chimney while easy to make self supporting, would have too much drag from wind.

I also didn't realize how far synthetics had come. While not yet capable of building a beanstalk, tethering a stratospheric balloon doesn't look unreasonable. Kevlar runs 1.5 g/cm3
So a 1 cm rope runs ~1g/cm, or about 100 kg/km.
3/8 rope is close to 1 cm. and it's rated at 12000 lbs -- call it 5500 kg*g or about 55 kN

So the support length of kevlar is about 55 kilometers.

Ok. Somewhere I goofed. This source https://en.wikipedia.org/wiki/Specific_strengthhttps://en.wikipedia.org/wiki/Specific_strength says that kevlar has a support length in excess of 250 km.

Ah: Rope isn't solid. I assumed a solid density, but used strength tables from real rope. But specific strength doesn't consider the mechanics of rope making.
1/2" rope has a breaking strength of 31,000 lbs and weighs 7.8 lbs/100 ft.

= 116 kg/km

So a a bit over metric ton gets you up to 10 km altitude. 2 metric tons at a 30 degree angle. Still gives you 25,000 pounds potential drag without breaking the rope.

Ok, why aren't we doing stratospheric wind turbines yet?

 

[jrmichler]

Our aim should be to debunk the meme before it spreads like a virus to consume other peoples lives and resources.

This.

Long tethers can be designed as constant stress tethers. The cross section increases with altitude so as to keep the stress constant. This allows a tether to be longer than the support length and still carry a load.

If anybody got serious about tethers extending up into the stratosphere, they would run into the ICAO (International Civil Aviation Organization) and the IATA (International Air Transport Association).

 

[Baluncore]

Ok, why aren't we doing stratospheric wind turbines yet?

Because WE are not a megalomaniac with infinite funding to waste on a massive failure.
Because wind turbines on the ground are lower technology and cost less to install and maintain.

You need to study the economics of all the possible alternatives. The cost of insurance, the probability of collision, storm damage and terrorism, along with the cost of decommissioning or wreckage removal and damage claims after a failure need to be considered.

By all means design a tether, but don't kid yourself that the tether is the only limiting factor on the project. Maybe like others before, you have acquired a fixation on a fabulous and magnificently uneconomic solution. Those whom the gods wish to destroy they first make insane.

 

[Sherwood Botsford]

One of the problems constantly cited against wind power is the lack of reliability. High altitude wind is far more predictable. Yes, to determine if it is viable you need to do comparisons to other technologies, and to the impacts on living next to a station. The good sites for wind power are relatively rare. While taller towers are more effective, they are also not appreciated by neighbours.

At the time I first read about HAWT tech the problem was tethering. I discovered that tethering was no longer the limiting factor.

Potential problems -- there are many. Here are a few:
* If you have a 20 km tether, what happens if the upper end fails? You have a non-trivial line falling down. Do you have to buy all the land in a large radius circle? Post a huge bond? Put the ground station on small islands 50 miles out to sea? Isolated stations in wilderness?
* How do you deal with aircraft? A new class of air space zone? Small transponders along the cable so they are visible to aircraft?
* What are effective upper end devices? Balloons? Tethered aircraft?

What are the alternatives that can provide predictable power, without greenhouse gas emissions?
* Massive interconnects -- the wind is blowing somewhere. Significant line losses if you are move energy from Oklahoma to New York.
* Nuclear. (Require a lot of concrete -- which releases large amounts of CO2 to make.)
* Geothermal.
* Battery -- see Tesla project in Austrailia
* Pumped storage -- sites uncommon.
* Other chemical storage -- hydrogen, methane... Poor cycle efficiency.
* Compressed air storage. Poor cycle efficiency.