Sunshade for the Planet

A UA professor's idea on how to reduce global warming is getting a lot of attention

If problems associated with global warming rage out of control, then Dr. Roger Angel has an idea that could quite literally have it covered.

Angel, 65, has proposed sending countless tiny shades into space that would refract some of the sunlight headed toward Earth. With less sunlight, there'd be less heating--counteracting the warming caused by carbon dioxide emissions. Using the sunshade as a reserve option--in conjunction with limiting the release of carbon dioxide--he said it would be possible to reduce the warming effect to "pre-industrial levels" if sudden, disastrous climate change seems unavoidable.

"I'm not sitting here, the mad scientist, trying to figure out how to let oil companies make more money," said Angel with a laugh. "I've been given this analogy that everything you need to know, you learned in kindergarten, or whatever it is--right? Some of the ground rules are: Tidy up your mess, and leave it the way you find it. Well, we're not doing that for this planet at the moment. We're making the most enormous mess."

Angel, a University of Arizona regents' professor and one of the world's foremost minds in modern optics, directs the Steward Observatory Mirror Laboratory and the Center for Astronomical Adaptive Optics. He's seen many of his visions become reality over the years. In fact, a segment of the mirror for the largest telescope in existence, which he helped design, is currently being constructed at the UA.

Angel's ideas have recently been covered in a variety of media, from an article about his legacy in The Arizona Republic to an interview with Robert Siegel on National Public Radio's All Things Considered. Everyday enthusiasts have dissected his latest proposal in online bulletin boards and blogs.

While the sunshade idea is nowhere near reality right now, the NASA Institute for Advanced Concepts, which "seeks proposals for revolutionary aeronautics and space concepts," has funded Angel's study on the feasibility and logistics of the concept.

Deploying the sunshade would be a costly, staggering effort aimed at reducing the amount of sunlight that reaches Earth by 2 percent. It would require new ways of getting payloads into space. But Angel has some elegant ideas about how to circumvent these issues.

As for the payload problem: Rockets from Earth would be out. Too expensive. Conventional thinking reasons that large masses could be constructed on the moon, and then sent up from there, which is cheaper than launching from Earth, because the moon's gravity exerts less force. But that has snags, too, Angel concluded.

"If you want to orbit 10,000 tons a day or something, which is what you'd have to do even to make progress with this problem over 10 years--it's thousands of tons a day to make the shades," he said. "That's basically put this thing virtually into the realm of science fiction, because even if we go back to the moon now, we're not going to build the capacity for thousands of tons a day of mining and processing and launching and whatever."

With these limitations in mind, Angel first concentrated on the sunshade material. He said he thinks he's found a way to construct the shades that's about 10 times less massive than previously imagined.

"But it's still 20 million tons," he said, "and that's still ruled out rockets. However, there's a technology that's been floating around since, you know, the '30s--so it's like 70 years old--which is to launch stuff by a magnetic force rather than a rocket force."

Using magnetic force to launch spacecraft costs several orders of magnitude less than rocketry, Angel said, yet it's never been implemented. He believes that's because while overall energy requirements are low, the energy has to be stored and released in a fraction of a second.

A rocket can keep accelerating and releasing energy until it's well away from the planet, but a launch using magnetic force must have all the energy pent up and released almost instantaneously, he said. The capital costs of using a power plant or two to store energy for a spell are very high, unless there are a lot of launches, according to Angel.

The spacecraft would need to be simple--without fragile components--to survive the g-force that would be exerted on them in a magnetic-force launch. They would also need to be sent higher than a low-Earth orbit, which exposes objects to a tremendous amount of heat from moving through air as they travel somewhat tangentially around the planet, he said.

"So magnetic launch is only useful in vast quantities; it's only useful for stuff that can stand 4,000 g, and it's no good for going into low-Earth orbit," Angel said. "But, if you want to launch millions of tons, if your stuff can take 4,000 g, and you want to go high, which is where I want it, then it looks great. Looks like you can now seriously and realistically think about launching from the Earth."

The sunshade--a "very big thing"--doesn't have to be a single structure, Angel continued. The assembly of the orbiting International Space Station from small pieces made him think that perhaps it would be a good idea to use little things that could act as a single unit.

Each spacecraft would be made of thin film, 2 feet in diameter, with "three little ears," mirrors and a solar sail about the size of a pocket calculator attached. It would contain a rudimentary global positioning system and have "little eyeballs" that look at the sun and look at the Earth so it knows where it is, Angel said.

"The individual spacecraft I love, because they are small," he said. "It's like an optical film that when you look through it, it's a bit blurry. You can still see stuff through it, and the sunlight going through it just gets bent by a couple of degrees."

The spacecraft would weigh a mere 1.4 grams each. In comparison, a Monarch butterfly weighs half a gram, while a hummingbird weighs about twice as much as the craft. About 14 trillion of them, each costing 7 cents, would be arranged in a cloud-like formation, Angel said.

The craft would need to be placed in space about 1 million miles from Earth. This "sweet spot," as Angel called it, is known as the Earth-Sun Lagrange L1 point. It's the position at which the gravitational pull from Earth roughly equals the pull from the Sun, allowing any objects placed there to maintain their distance from the planet.

"It's the obvious place you'd want to put something," Angel said. "Now, unfortunately, unlike, say, the moon's orbit, which goes on for billions of years, if you get something exactly on the sweet spot, it will stay there; but if it just wanders off a little bit, it's like rolling off the top of a ball. It goes faster and faster--so it's not a stable orbit."

Satellites today contain rockets to give them a little push and prevent their orbits from decaying, but that's not something that would be feasible for the sunshade spacecraft, Angel said. Instead, he envisions using the sails to harness sunlight's "pressure," which exerts a weak force, to keep the spacecraft in place.

The projected price tag is $3 trillion, Angel said, which is perhaps worth it when considering that Swiss Re, one of the world's largest insurers, is sweating over projections that natural disasters spurred by climate change could soon inflict $150 billion worth of damage annually.

"It's like 1 or 2 percent of world GNP in the next 20 years," he said. "The planet is worth that for sure."

Whether the planet is indeed worth that is a hypothetical political and economic consideration at this point. In the meantime, however, Angel is writing up the specifics of his vision for a scholarly journal. He has no illusions about his futuristic idea being a magic bullet to end the threat of global warming.

"There is no easy solution," he said. "Basically, you've got a planet which is addicted to energy. There's no way to change that quickly.

"But I've got a 3-year-old granddaughter, and I don't want to leave this planet a huge mess for that generation to fix up."

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