Big Ideas in Small Packages

You might say that's what nanotechnology is all about -- big ideas in small packages. By building up from the bottom with atoms and molecules, the fundamental building blocks of nature, we can anticipate making huge changes in the world. How we handle that new power over materials and manufacturing is, of course, the subject of this blog and the work of the Center for Responsible Nanotechnology.

Here's someone else offering big ideas contained in small packages:

For the past year, University of Arizona astronomer Roger Angel has been looking at ways to cool the Earth in an emergency. He's been studying the practicality of deploying a space sunshade in a global warming crisis, a crisis where it becomes clear that Earth is unmistakably headed for disastrous climate change within a decade or two. . .

Angel is now publishing a first detailed, scholarly paper, "Feasibility of cooling the Earth with a cloud of small spacecraft near L1," in the Proceedings of the National Academy of Sciences. The plan would be to launch a constellation of trillions of small free-flying spacecraft a million miles above Earth into an orbit aligned with the sun, called the L-1 orbit.

The spacecraft would form a long, cylindrical cloud with a diameter about half that of Earth, and about 10 times longer. About 10 percent of the sunlight passing through the 60,000-mile length of the cloud, pointing lengthwise between the Earth and the sun, would be diverted away from our planet. The effect would be to uniformly reduce sunlight by about 2 percent over the entire planet, enough to balance the heating of a doubling of atmospheric carbon dioxide in Earth's atmosphere. . .

"The earlier ideas were for bigger, heavier structures that would have needed manufacture and launch from the moon, which is pretty futuristic," Angel said. "I wanted to make the sunshade from small 'flyers,' small, light and extremely thin spacecraft that could be completely assembled and launched from Earth, in stacks of a million at a time. When they reached L1, they would be dealt off the stack into a cloud. There's nothing to assemble in space."

The lightweight flyers designed by Angel would be made of a transparent film pierced with small holes. Each flyer would be two feet in diameter, 1/5000 of an inch thick and weigh about a gram, the same as a large butterfly. It would use "MEMS" technology mirrors as tiny sails that tilt to hold the flyers position in the orbiting constellation. The flyer's transparency and steering mechanism prevent it from being blown away by radiation pressure. Radiation pressure is the pressure from the sun's light itself.

The total mass of all the fliers making up the space sunshade structure would be 20 million tons. At $10,000 a pound, conventional chemical rocket launch is prohibitively expensive. Angel proposes using a cheaper way developed by Sandia National Laboratories for electromagnetic space launchers, which could bring cost down to as little as $20 a pound.

The sunshade could be deployed by a total 20 electromagnetic launchers launching a stack of flyers every 5 minutes for 10 years. The electromagnetic launchers would ideally run on hydroelectric power, but even in the worst-case environmental scenario with coal-generated electricity, each ton of carbon used to make electricity would mitigate the effect of 1000 tons of atmospheric carbon.

If signs of catastrophic worldwide climate and ecosystem changes caused by global warming keep getting clearer in years to come, as we expect they will, then big solutions will be needed desperately. Perhaps Angel's trillion flyers is one of them.

Mike Treder

Tags: nanotechnology nanotech nano science technology ethics weblog blog

Comments

[Tom Craver]

20M tons, at 1000000 shades/ton - so he's planning on 20 trillion of these devices, each with an area of about 0.4m^2, or about 8 million sqkm - i.e. about 10% of the earth's solar intercept cross-section.

Since he's aiming to cut light by 2%, his refractive approach is about 20% as efficient as using reflectors.

He apparently has the sunshades dynamically use sunlight pressure to maintain position between the sun and Earth - but he deliberately made the shades very non-reflective so that photonic pressure wouldn't quickly blow them away.

Making the shades refractive won't prevent interaction with the solar wind - does anyone have access to the full PNAS paper, to check if he took that into consideration?

And as long as he's putting intelligence on board, why not have them balance gravity, sunlight, solar wind, position etc? Then they could be reflective and near 100% efficient, reducing the mass to 4 million tons. They might be thinner as well, further shaving the mass.

[Tom Craver]

One way to amplify the effects of space sunshades, would be to cool the sea near Earth's poles - increasing ice cover, and countering a strong global warming feedback loop. That should give on the order of a 8x gain (albedo of snow = 0.8 vs seawater's 0.1). But it might not work with his refractive rather than reflective shades.

It'd still be cheaper, even with $20/kg launch costs, to use reflectors floating high in earth's atmosphere, with just enough smarts on board to stay at a specified altitude and maybe the a fixed latitude (to use the ice leveraging scheme).

[Matt]

I hope that "big solutions [that] will be desparately needed" do not only include absurdly oversized mega-engineering (running out of superlatives here), but also political, inconvenient, almost boring solutions like international agreement on lowering harmful emission which are actually enforced. Otherwise, hypothetical international regulation of MM, which is the only possible kind of MM regulation, wouldn't stand a chance.

[Hal]

Physicist Gregory Benford proposed injecting particles into the stratosphere over the polar regions to preferentially cool those areas (save the polar bears!). It is much cheaper to focus on smaller areas like that, not to mention this technology is basically feasible today. Wind currents allow the aerosols to remain concentrated over the poles, and they would rain out every year so if things went wrong the experiment could be stopped.

http://www.desmogblog.com/gregory-benford-audio-interview