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Innovation

# A \$2,500 billion sun umbrella?

A University of Arizona professor thinks he has a solution to protect us from the global warming effect. He wants to reduce the temperature on Earth by building a massive space sunshade made of -- hold your breath -- 20,000 billions of very small spacecraft weighing about a gram and orbiting a million miles above our heads.
Written by Roland Piquepaille, Inactive

Roger Angel, who works at the Department of Astronomy of the University of Arizona as Director of the Steward Observatory Mirror Laboratory and the Center for Astronomical Adaptive Optics, received a grant from the NASA Institute for Advanced Concepts in July 2006 to do further research about this idea.

Before looking at more details about this gigantic project, here is an image showing a cloud of small spacecraft near the inner Lagrange point (L1) if they're launched in the future (Credit: Roger Angel, UA Steward Observatory; link to a larger version).

So how would this sunshade work?

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.

And now, are you ready for big numbers?

• 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. Not really a big number? Consider how many would be needed.
• To build such a cloud, 20,000 billions 'butterflies' would need to be sent into space.
• This would represent about 20 million tons.
• And even with the electromagnetic space launchers developed at Sandia National Laboratories which promise to send objects in space for about \$20 per pound, the total cost wold be about \$1,000 billion. Except if I made a mistake...
• Of course, you will need to launch these trillion spacecraft. In "A Swarm of Umbrellas vs. Global Warming," Science News Online writes: "With each such launch sending out 800,000 flyers, the project would require 20 million launches over a decade."
• And Angel summarizes the costs: "It could be developed and deployed in about 25 years at a cost of a few trillion dollars. With care, the solar shade should last about 50 years. So the average cost is about \$100 billion a year, or about two-tenths of one percent of the global domestic product."
• Even if these numbers look -- rightly -- astronomic -- please remember that the monthly U.S. trade deficit is in the \$60 to \$70 billion range -- per month!

Anyway, I don't think that a single government would launch such a program. It would certainly cost less to develop renewable energy.

For those of you who think that I'm a victim of an April Fool's Day joke, this research work has been published by the Proceedings of the National Academy of Sciences under the name "Feasibility of cooling the Earth with a cloud of small spacecraft near the inner Lagrange point (L1)" (November 3, 2006). Here is a link to the abstract.

So will we be protected one day from global warming by this massive space sunshade? I don't really believe it. But what do you think?

Sources: Lori Stiles, University of Arizona News, November 3, 2006; and various websites

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