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SCIENCE SOLAR ENERGY : Sunlight Gathered Up as a Tool of the Future

TIMES SCIENCE WRITER

Remember the mean little kid who used to set fire to scraps of paper with a magnifying glass and a little help from the sun?

Well, he’s back, but this time he’s a lot better armed.

Applying state-of-the-art technology to that old trick has enabled scientists in Southern California and Illinois to begin harnessing the sun’s light and heat in ways that could have many diverse applications in the future. In the latest step, announced today, University of Chicago scientists report that they have produced the highest intensity of sunlight found anywhere in the solar system.

The advancing technology could be used to rapidly send large amounts of data between orbiting satellites, to zap toxic substances on Earth with such intensity that they would be rendered harmless, or even to melt the soil on the surface of the moon for use in building landing pads and radiation shelters.

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The concentration of sunlight by the Chicago team was 15% higher than on the surface of the sun.

“We even beat the sun,” said physicist Dave Cooke, lead author of a report in today’s issue of the British scientific journal Nature.

By using a small mirror and a “collector” that funnels sunlight into an intense beam, the Chicago team concentrated sunlight to 84,000 times its normal intensity on Earth.

Meanwhile, teams of researchers in California have built a huge solar collector that concentrates sunlight so intensely that if it were on the moon it could melt the soil on the lunar surface. Laboratory experiments show that the process would produce shiny black glass that could be used to manufacture composite materials for construction projects on the moon.

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The giant collector, which uses 82 mirrors of one square meter each, has produced temperatures of 2,200 to 2,400 degrees Fahrenheit, according to engineers with McDonnell Douglas Space Systems Co. of Huntington Beach. The collector was built by the firm in the early 1980s to use the sun’s power to produce electricity, but it was abandoned when the price of oil plummeted later that decade.

Ironically, it has been called back into service at the height of another Middle East crisis--but for a very different reason.

Engineers with the firm have teamed up with ALCOA/Golds-worth Engineering of Torrance and the Space Studies Institute of Princeton, N.J., to see if the huge collector could be used to help astronauts build structures they will need on the moon.

“The idea is to learn more about design and application, to see if we can simplify it,” said John Garvey, project manager at McDonnell Douglas. Garvey believes it might be possible to build a solar collector that could be transported to the moon and used there to melt soil into fibers and glass “bricks” that could be used in construction.

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“The beauty of this is that all your material is on the moon,” and that could reduce the need to transport construction materials from Earth, he said.

Solar energy could be used more efficiently on the moon than on Earth because the absence of a lunar atmosphere would allow 40% more sunlight to reach the collectors, the engineers said. And since there is no wind, support facilities could be much lighter than on Earth.

The engineers tested their concept using simulated lunar soil supplied by the Princeton group. When subjected to intense heat, it melted into glass, Garvey said. Since the temperatures were so high, special crucibles to hold the molten “glass” were supplied by the Torrance firm.

“You could even make forks and spoons (or almost anything else the astronauts would need) if you have the right molds” to pour the glass into, said engineer Mike Magoffin.

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The engineers came up with the idea after President Bush called for building a permanent station on the moon, a feat that most experts believe can best be done if lunar materials are used for much of the construction.

Congress recently eliminated funds from the current budget for the President’s “Space Exploration Initiative,” of which the lunar outpost is a part, but the White House is still pushing the project.

Scientists at the University of Chicago are more down to Earth in their work, but it is just about as far out.

Unlike the huge McDonnell Douglas facility, the Chicago team uses an ordinary telescope mirror of 16-inch diameter. The parabolic mirror reflects sunlight into a narrow beam that passes through a “concentrator,” which is just a “funnel for light,” Cooke said during a telephone interview.

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The funnel, which is a precisely machined cone of pure sapphire, bends the incoming light rays as they reflect off its sides, thus concentrating it further. Sapphire was picked because it has a high refractive index, or ability to bend light, that is so great that it does not even have to be coated with a reflective material.

The result is a highly efficient solar collector, according to the University of Chicago’s Roland Winston, chairman of the physics department, who pioneered in the field.

Last winter, the researchers tested their equipment atop the physics building. The solar collector generated 72 watts per square millimeter of surface. Sunlight reaching Earth normally generates less than one-thousandth of a watt per square millimeter.

Cooke said such an intense beam could be used as a “solar pumped laser,” thus generating a concentrated beam of light that would be so powerful it could break down toxic wastes. In space, the beam of light could be used as a carrier to transmit immense amounts of data between communications satellites, he added.

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The technology could also be used to generate extremely high temperatures for processing materials, similar to what the Southern California researchers have in mind for the surface of the moon.

Incidentally, the technology could also be used to generate electricity, thus easing demand for foreign oil, the researchers said. That idea was abandoned earlier when the price of oil dropped, but Garvey said that concept could be resurrected.


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